diff --git a/app/controllers/api/v1/collection_weapons_controller.rb b/app/controllers/api/v1/collection_weapons_controller.rb
index ea8a75f..0869c02 100644
--- a/app/controllers/api/v1/collection_weapons_controller.rb
+++ b/app/controllers/api/v1/collection_weapons_controller.rb
@@ -177,7 +177,8 @@ module Api
           :weapon_id, :uncap_level, :transcendence_step,
           :weapon_key1_id, :weapon_key2_id, :weapon_key3_id, :weapon_key4_id,
           :awakening_id, :awakening_level,
-          :ax_modifier1, :ax_strength1, :ax_modifier2, :ax_strength2,
+          :ax_modifier1_id, :ax_strength1, :ax_modifier2_id, :ax_strength2,
+          :befoulment_modifier_id, :befoulment_strength, :exorcism_level,
           :element
         )
       end
@@ -187,7 +188,8 @@ module Api
           :weapon_id, :uncap_level, :transcendence_step,
           :weapon_key1_id, :weapon_key2_id, :weapon_key3_id, :weapon_key4_id,
           :awakening_id, :awakening_level,
-          :ax_modifier1, :ax_strength1, :ax_modifier2, :ax_strength2,
+          :ax_modifier1_id, :ax_strength1, :ax_modifier2_id, :ax_strength2,
+          :befoulment_modifier_id, :befoulment_strength, :exorcism_level,
           :element
         ])
       end
diff --git a/app/controllers/api/v1/grid_weapons_controller.rb b/app/controllers/api/v1/grid_weapons_controller.rb
index 7188dc0..984f698 100644
--- a/app/controllers/api/v1/grid_weapons_controller.rb
+++ b/app/controllers/api/v1/grid_weapons_controller.rb
@@ -291,13 +291,13 @@ module Api
       ##
       # Normalizes the AX modifier fields for the weapon parameters.
       #
-      # Sets ax_modifier1 and ax_modifier2 to nil if their integer values equal -1.
+      # Sets ax_modifier1_id and ax_modifier2_id to nil if their integer values equal -1.
       #
       # @return [void]
       def normalize_ax_fields!
-        params[:weapon][:ax_modifier1] = nil if weapon_params[:ax_modifier1].to_i == -1
-
-        params[:weapon][:ax_modifier2] = nil if weapon_params[:ax_modifier2].to_i == -1
+        params[:weapon][:ax_modifier1_id] = nil if weapon_params[:ax_modifier1_id].to_i == -1
+        params[:weapon][:ax_modifier2_id] = nil if weapon_params[:ax_modifier2_id].to_i == -1
+        params[:weapon][:befoulment_modifier_id] = nil if weapon_params[:befoulment_modifier_id].to_i == -1
       end
 
       ##
@@ -515,7 +515,8 @@ module Api
           :id, :party_id, :weapon_id, :collection_weapon_id,
           :position, :mainhand, :uncap_level, :transcendence_step, :element,
           :weapon_key1_id, :weapon_key2_id, :weapon_key3_id,
-          :ax_modifier1, :ax_modifier2, :ax_strength1, :ax_strength2,
+          :ax_modifier1_id, :ax_modifier2_id, :ax_strength1, :ax_strength2,
+          :befoulment_modifier_id, :befoulment_strength, :exorcism_level,
           :awakening_id, :awakening_level
         )
       end
diff --git a/app/controllers/api/v1/weapon_stat_modifiers_controller.rb b/app/controllers/api/v1/weapon_stat_modifiers_controller.rb
new file mode 100644
index 0000000..235e629
--- /dev/null
+++ b/app/controllers/api/v1/weapon_stat_modifiers_controller.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+module Api
+  module V1
+    class WeaponStatModifiersController < Api::V1::ApiController
+      # GET /weapon_stat_modifiers
+      def index
+        @modifiers = WeaponStatModifier.all
+        @modifiers = @modifiers.where(category: params[:category]) if params[:category].present?
+
+        render json: WeaponStatModifierBlueprint.render(@modifiers, root: :weapon_stat_modifiers)
+      end
+
+      # GET /weapon_stat_modifiers/:id
+      def show
+        @modifier = WeaponStatModifier.find(params[:id])
+        render json: WeaponStatModifierBlueprint.render(@modifier)
+      end
+    end
+  end
+end
diff --git a/config/routes.rb b/config/routes.rb
index d417622..bffdfe4 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -128,6 +128,7 @@ Rails.application.routes.draw do
         get 'for_slot/:slot', action: :for_slot, as: :for_slot
       end
     end
+    resources :weapon_stat_modifiers, only: %i[index show]
 
     # Grid artifacts
     resources :grid_artifacts, only: %i[create update destroy] do
diff --git a/db/seeds/weapon_stat_modifiers.rb b/db/seeds/weapon_stat_modifiers.rb
new file mode 100644
index 0000000..ad4e0a1
--- /dev/null
+++ b/db/seeds/weapon_stat_modifiers.rb
@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+##
+# Seeds for WeaponStatModifier - AX skills and befoulments
+#
+
+puts 'Seeding weapon stat modifiers...'
+
+ax_skills = [
+  # Primary AX Skills
+  { slug: 'ax_hp', name_en: 'HP', name_jp: 'HP', category: 'ax', stat: 'hp', polarity: 1, suffix: '%', base_min: 1, base_max: 11, game_skill_id: 1588 },
+  { slug: 'ax_atk', name_en: 'ATK', name_jp: '攻撃', category: 'ax', stat: 'atk', polarity: 1, suffix: '%', base_min: 1, base_max: 3.5, game_skill_id: 1589 },
+  { slug: 'ax_def', name_en: 'DEF', name_jp: '防御', category: 'ax', stat: 'def', polarity: 1, suffix: '%', base_min: 1, base_max: 8, game_skill_id: 1590 },
+  { slug: 'ax_ca_dmg', name_en: 'C.A. DMG', name_jp: '奥義ダメ', category: 'ax', stat: 'ca_dmg', polarity: 1, suffix: '%', base_min: 2, base_max: 8.5, game_skill_id: 1591 },
+  { slug: 'ax_multiattack', name_en: 'Multiattack Rate', name_jp: '連撃率', category: 'ax', stat: 'multiattack', polarity: 1, suffix: '%', base_min: 1, base_max: 4, game_skill_id: 1592 },
+
+  # Secondary AX Skills
+  { slug: 'ax_debuff_res', name_en: 'Debuff Resistance', name_jp: '弱体耐性', category: 'ax', stat: 'debuff_res', polarity: 1, suffix: '%', base_min: 1, base_max: 3, game_skill_id: 1593 },
+  { slug: 'ax_ele_atk', name_en: 'Elemental ATK', name_jp: '全属性攻撃力', category: 'ax', stat: 'ele_atk', polarity: 1, suffix: '%', base_min: 1, base_max: 5, game_skill_id: 1594 },
+  { slug: 'ax_healing', name_en: 'Healing', name_jp: '回復性能', category: 'ax', stat: 'healing', polarity: 1, suffix: '%', base_min: 2, base_max: 5, game_skill_id: 1595 },
+  { slug: 'ax_da', name_en: 'Double Attack Rate', name_jp: 'DA確率', category: 'ax', stat: 'da', polarity: 1, suffix: '%', base_min: 1, base_max: 2, game_skill_id: 1596 },
+  { slug: 'ax_ta', name_en: 'Triple Attack Rate', name_jp: 'TA確率', category: 'ax', stat: 'ta', polarity: 1, suffix: '%', base_min: 1, base_max: 2, game_skill_id: 1597 },
+  { slug: 'ax_ca_cap', name_en: 'C.A. DMG Cap', name_jp: '奥義上限', category: 'ax', stat: 'ca_cap', polarity: 1, suffix: '%', base_min: 1, base_max: 2, game_skill_id: 1599 },
+  { slug: 'ax_stamina', name_en: 'Stamina', name_jp: '渾身', category: 'ax', stat: 'stamina', polarity: 1, suffix: nil, base_min: 1, base_max: 3, game_skill_id: 1600 },
+  { slug: 'ax_enmity', name_en: 'Enmity', name_jp: '背水', category: 'ax', stat: 'enmity', polarity: 1, suffix: nil, base_min: 1, base_max: 3, game_skill_id: 1601 },
+
+  # Extended AX Skills (axType 2)
+  { slug: 'ax_skill_supp', name_en: 'Supplemental Skill DMG', name_jp: 'アビ与ダメ上昇', category: 'ax', stat: 'skill_supp', polarity: 1, suffix: nil, base_min: 1, base_max: 5, game_skill_id: 1719 },
+  { slug: 'ax_ca_supp', name_en: 'Supplemental C.A. DMG', name_jp: '奥義与ダメ上昇', category: 'ax', stat: 'ca_supp', polarity: 1, suffix: nil, base_min: 1, base_max: 5, game_skill_id: 1720 },
+  { slug: 'ax_ele_dmg_red', name_en: 'Elemental DMG Reduction', name_jp: '属性ダメ軽減', category: 'ax', stat: 'ele_dmg_red', polarity: 1, suffix: '%', base_min: 1, base_max: 5, game_skill_id: 1721 },
+  { slug: 'ax_na_cap', name_en: 'Normal ATK DMG Cap', name_jp: '通常ダメ上限', category: 'ax', stat: 'na_cap', polarity: 1, suffix: '%', base_min: 0.5, base_max: 1.5, game_skill_id: 1722 },
+
+  # Utility AX Skills (axType 3)
+  { slug: 'ax_exp', name_en: 'EXP Gain', name_jp: 'EXP UP', category: 'ax', stat: 'exp', polarity: 1, suffix: '%', base_min: 5, base_max: 10, game_skill_id: 1837 },
+  { slug: 'ax_rupie', name_en: 'Rupie Gain', name_jp: '獲得ルピ', category: 'ax', stat: 'rupie', polarity: 1, suffix: '%', base_min: 10, base_max: 20, game_skill_id: 1838 }
+]
+
+befoulments = [
+  # Befoulments - game_skill_ids will be populated as we discover them
+  { slug: 'befoul_atk_down', name_en: 'ATK Down', name_jp: '攻撃力DOWN', category: 'befoulment', stat: 'atk', polarity: -1, suffix: '%', base_min: -12, base_max: -6, game_skill_id: nil },
+  { slug: 'befoul_def_down', name_en: 'DEF Down', name_jp: '防御力DOWN', category: 'befoulment', stat: 'def', polarity: -1, suffix: '%', base_min: -25, base_max: -21, game_skill_id: 2880 },
+  { slug: 'befoul_da_ta_down', name_en: 'DA/TA Down', name_jp: '連撃率DOWN', category: 'befoulment', stat: 'da_ta', polarity: -1, suffix: '%', base_min: -22, base_max: -19, game_skill_id: nil },
+  { slug: 'befoul_ca_dmg_down', name_en: 'CA DMG Down', name_jp: '奥義ダメージDOWN', category: 'befoulment', stat: 'ca_dmg', polarity: -1, suffix: '%', base_min: -38, base_max: -26, game_skill_id: nil },
+  { slug: 'befoul_dot', name_en: 'Damage Over Time', name_jp: '毎ターンダメージ', category: 'befoulment', stat: 'dot', polarity: -1, suffix: '%', base_min: 6, base_max: 16, game_skill_id: nil },
+  { slug: 'befoul_hp_down', name_en: 'Max HP Down', name_jp: '最大HP減少', category: 'befoulment', stat: 'hp', polarity: -1, suffix: '%', base_min: -50, base_max: -26, game_skill_id: nil },
+  { slug: 'befoul_debuff_down', name_en: 'Debuff Success Down', name_jp: '弱体成功率DOWN', category: 'befoulment', stat: 'debuff_success', polarity: -1, suffix: '%', base_min: -16, base_max: -6, game_skill_id: nil },
+  { slug: 'befoul_ability_dmg_down', name_en: 'Ability DMG Down', name_jp: 'アビリティダメージDOWN', category: 'befoulment', stat: 'ability_dmg', polarity: -1, suffix: '%', base_min: -50, base_max: -50, game_skill_id: nil }
+]
+
+(ax_skills + befoulments).each do |attrs|
+  modifier = WeaponStatModifier.find_or_initialize_by(slug: attrs[:slug])
+  modifier.assign_attributes(attrs)
+  modifier.save!
+end
+
+puts "Created/updated #{WeaponStatModifier.count} weapon stat modifiers"
diff --git a/docs/planning/befoulments-feature-plan.md b/docs/planning/befoulments-feature-plan.md
new file mode 100644
index 0000000..4cd3814
--- /dev/null
+++ b/docs/planning/befoulments-feature-plan.md
@@ -0,0 +1,671 @@
+# Befoulments & WeaponStatModifier Consolidation
+
+## Overview
+
+Implement Befoulments (魔蝕) and consolidate with AX skills using a new `WeaponStatModifier` table.
+
+### Terminology
+- **Odiant (禁禍武器)** = A weapon series that has befoulments instead of AX skills
+- **Befoulments (魔蝕)** = Negative stat augments that appear on Odiant weapons
+- **Exorcism Level (退魔Lv)** = Level 0-5 that reduces befoulment strength
+
+**Key insight:** `augment_skill_info` contains:
+- **AX skills** for regular weapons (`is_odiant_weapon: false`)
+- **Befoulments** for Odiant weapons (`is_odiant_weapon: true`)
+
+They are mutually exclusive - a weapon has either AX skills OR befoulments, never both.
+
+---
+
+## Database Schema
+
+### 1. New Table: `weapon_stat_modifiers`
+
+Centralized definition of all weapon stat modifiers (AX skills + befoulments):
+
+```ruby
+create_table :weapon_stat_modifiers do |t|
+  t.string :slug, null: false, index: { unique: true }  # 'ax_atk', 'befoul_def_down'
+  t.string :name_en, null: false
+  t.string :name_jp
+  t.string :category, null: false      # 'ax' or 'befoulment'
+  t.string :stat                       # 'atk', 'def', 'da_ta', 'ca_dmg', 'hp', 'dot', etc.
+  t.integer :polarity, default: 1      # 1 = buff, -1 = debuff
+  t.string :suffix                     # '%' for percentages, nil for flat values
+  t.float :base_min                    # Known min initial value (informational)
+  t.float :base_max                    # Known max initial value (informational)
+  t.integer :game_skill_id             # Maps to game's skill_id for import
+  t.timestamps
+end
+```
+
+**Icon convention:** Frontend derives icon path from `slug`:
+- `ax_atk` → `weapon-stat-modifier/ax_atk.png`
+- `befoul_def_down` → `weapon-stat-modifier/befoul_def_down.png`
+
+Rename game icons (e.g., `ex_skill_def_down` → `befoul_def_down`) to match slugs.
+
+### 2. Refactor AX & Add Befoulment Columns (Foreign Keys)
+
+Replace raw integer `ax_modifier1/2` with foreign keys, and add befoulment FK:
+
+```ruby
+# collection_weapons
+# Remove old integer columns
+remove_column :collection_weapons, :ax_modifier1, :integer
+remove_column :collection_weapons, :ax_modifier2, :integer
+
+# Add FK columns referencing weapon_stat_modifiers
+add_reference :collection_weapons, :ax_modifier1, foreign_key: { to_table: :weapon_stat_modifiers }
+add_reference :collection_weapons, :ax_modifier2, foreign_key: { to_table: :weapon_stat_modifiers }
+add_reference :collection_weapons, :befoulment_modifier, foreign_key: { to_table: :weapon_stat_modifiers }
+add_column :collection_weapons, :befoulment_strength, :float
+add_column :collection_weapons, :exorcism_level, :integer, default: 0
+
+# grid_weapons - same pattern
+add_reference :grid_weapons, :ax_modifier1, foreign_key: { to_table: :weapon_stat_modifiers }
+add_reference :grid_weapons, :ax_modifier2, foreign_key: { to_table: :weapon_stat_modifiers }
+add_reference :grid_weapons, :befoulment_modifier, foreign_key: { to_table: :weapon_stat_modifiers }
+add_column :grid_weapons, :befoulment_strength, :float
+add_column :grid_weapons, :exorcism_level, :integer, default: 0
+```
+
+### 2b. Data Migration for Existing AX Skills
+
+Migrate existing `ax_modifier1/2` integer values to FK references:
+
+```ruby
+# Run after weapon_stat_modifiers table is seeded
+CollectionWeapon.where.not(ax_modifier1: nil).find_each do |cw|
+  modifier = WeaponStatModifier.find_by(game_skill_id: cw.ax_modifier1)
+  cw.update_columns(ax_modifier1_id: modifier&.id) if modifier
+end
+
+CollectionWeapon.where.not(ax_modifier2: nil).find_each do |cw|
+  modifier = WeaponStatModifier.find_by(game_skill_id: cw.ax_modifier2)
+  cw.update_columns(ax_modifier2_id: modifier&.id) if modifier
+end
+
+# Same for GridWeapon
+```
+
+**Note:** Strength values (`ax_strength1/2`) are preserved as-is since they store the actual value.
+
+### 3. WeaponSeries `augment_type` Enum
+
+Replace `has_ax_skills` boolean with an enum that enforces mutual exclusivity:
+
+```ruby
+# Migration
+remove_column :weapon_series, :has_ax_skills, :boolean
+add_column :weapon_series, :augment_type, :integer, default: 0
+
+# Data migration
+WeaponSeries.where(has_ax_skills: true).update_all(augment_type: 1)
+```
+
+```ruby
+# Model
+enum :augment_type, { none: 0, ax: 1, befoulment: 2 }, default: :none
+
+scope :with_ax_skills, -> { where(augment_type: :ax) }
+scope :with_befoulments, -> { where(augment_type: :befoulment) }
+```
+
+---
+
+## Seed Data
+
+### AX Skill Modifiers (Complete List)
+
+All AX skills from game data with their game_skill_id values:
+
+```ruby
+WeaponStatModifier.create!([
+  # Primary AX Skills
+  { slug: 'ax_atk', name_en: 'ATK', name_jp: '攻撃', category: 'ax', stat: 'atk', polarity: 1, suffix: '%', base_min: 1, base_max: 3.5, game_skill_id: 1589 },
+  { slug: 'ax_def', name_en: 'DEF', name_jp: '防御', category: 'ax', stat: 'def', polarity: 1, suffix: '%', base_min: 1, base_max: 8, game_skill_id: 1590 },
+  { slug: 'ax_hp', name_en: 'HP', name_jp: 'HP', category: 'ax', stat: 'hp', polarity: 1, suffix: '%', base_min: 1, base_max: 11, game_skill_id: 1588 },
+  { slug: 'ax_ca_dmg', name_en: 'C.A. DMG', name_jp: '奥義ダメ', category: 'ax', stat: 'ca_dmg', polarity: 1, suffix: '%', base_min: 2, base_max: 8.5, game_skill_id: 1591 },
+  { slug: 'ax_multiattack', name_en: 'Multiattack Rate', name_jp: '連撃率', category: 'ax', stat: 'multiattack', polarity: 1, suffix: '%', base_min: 1, base_max: 4, game_skill_id: 1592 },
+
+  # Secondary AX Skills
+  { slug: 'ax_debuff_res', name_en: 'Debuff Resistance', name_jp: '弱体耐性', category: 'ax', stat: 'debuff_res', polarity: 1, suffix: '%', base_min: 1, base_max: 3, game_skill_id: 1593 },
+  { slug: 'ax_ele_atk', name_en: 'Elemental ATK', name_jp: '全属性攻撃力', category: 'ax', stat: 'ele_atk', polarity: 1, suffix: '%', base_min: 1, base_max: 5, game_skill_id: 1594 },
+  { slug: 'ax_healing', name_en: 'Healing', name_jp: '回復性能', category: 'ax', stat: 'healing', polarity: 1, suffix: '%', base_min: 2, base_max: 5, game_skill_id: 1595 },
+  { slug: 'ax_da', name_en: 'Double Attack Rate', name_jp: 'DA確率', category: 'ax', stat: 'da', polarity: 1, suffix: '%', base_min: 1, base_max: 2, game_skill_id: 1596 },
+  { slug: 'ax_ta', name_en: 'Triple Attack Rate', name_jp: 'TA確率', category: 'ax', stat: 'ta', polarity: 1, suffix: '%', base_min: 1, base_max: 2, game_skill_id: 1597 },
+  { slug: 'ax_ca_cap', name_en: 'C.A. DMG Cap', name_jp: '奥義上限', category: 'ax', stat: 'ca_cap', polarity: 1, suffix: '%', base_min: 1, base_max: 2, game_skill_id: 1599 },
+  { slug: 'ax_stamina', name_en: 'Stamina', name_jp: '渾身', category: 'ax', stat: 'stamina', polarity: 1, suffix: nil, base_min: 1, base_max: 3, game_skill_id: 1600 },
+  { slug: 'ax_enmity', name_en: 'Enmity', name_jp: '背水', category: 'ax', stat: 'enmity', polarity: 1, suffix: nil, base_min: 1, base_max: 3, game_skill_id: 1601 },
+
+  # Extended AX Skills (axType 2)
+  { slug: 'ax_skill_supp', name_en: 'Supplemental Skill DMG', name_jp: 'アビ与ダメ上昇', category: 'ax', stat: 'skill_supp', polarity: 1, suffix: nil, base_min: 1, base_max: 5, game_skill_id: 1719 },
+  { slug: 'ax_ca_supp', name_en: 'Supplemental C.A. DMG', name_jp: '奥義与ダメ上昇', category: 'ax', stat: 'ca_supp', polarity: 1, suffix: nil, base_min: 1, base_max: 5, game_skill_id: 1720 },
+  { slug: 'ax_ele_dmg_red', name_en: 'Elemental DMG Reduction', name_jp: '属性ダメ軽減', category: 'ax', stat: 'ele_dmg_red', polarity: 1, suffix: '%', base_min: 1, base_max: 5, game_skill_id: 1721 },
+  { slug: 'ax_na_cap', name_en: 'Normal ATK DMG Cap', name_jp: '通常ダメ上限', category: 'ax', stat: 'na_cap', polarity: 1, suffix: '%', base_min: 0.5, base_max: 1.5, game_skill_id: 1722 },
+
+  # Utility AX Skills (axType 3)
+  { slug: 'ax_exp', name_en: 'EXP Gain', name_jp: 'EXP UP', category: 'ax', stat: 'exp', polarity: 1, suffix: '%', base_min: 5, base_max: 10, game_skill_id: 1837 },
+  { slug: 'ax_rupie', name_en: 'Rupie Gain', name_jp: '獲得ルピ', category: 'ax', stat: 'rupie', polarity: 1, suffix: '%', base_min: 10, base_max: 20, game_skill_id: 1838 },
+])
+```
+
+### Befoulment Modifiers
+
+```ruby
+# game_skill_id values will be populated as we discover them - we know 2880 = DEF Down
+WeaponStatModifier.create!([
+  { slug: 'befoul_atk_down', name_en: 'ATK Down', name_jp: '攻撃力DOWN', category: 'befoulment', stat: 'atk', polarity: -1, suffix: '%', base_min: -12, base_max: -6 },
+  { slug: 'befoul_def_down', name_en: 'DEF Down', name_jp: '防御力DOWN', category: 'befoulment', stat: 'def', polarity: -1, suffix: '%', base_min: -25, base_max: -21, game_skill_id: 2880 },
+  { slug: 'befoul_da_ta_down', name_en: 'DA/TA Down', name_jp: '連撃率DOWN', category: 'befoulment', stat: 'da_ta', polarity: -1, suffix: '%', base_min: -22, base_max: -19 },
+  { slug: 'befoul_ca_dmg_down', name_en: 'CA DMG Down', name_jp: '奥義ダメージDOWN', category: 'befoulment', stat: 'ca_dmg', polarity: -1, suffix: '%', base_min: -38, base_max: -26 },
+  { slug: 'befoul_dot', name_en: 'Damage Over Time', name_jp: '毎ターンダメージ', category: 'befoulment', stat: 'dot', polarity: -1, suffix: '%', base_min: 6, base_max: 16 },
+  { slug: 'befoul_hp_down', name_en: 'Max HP Down', name_jp: '最大HP減少', category: 'befoulment', stat: 'hp', polarity: -1, suffix: '%', base_min: -50, base_max: -26 },
+  { slug: 'befoul_debuff_down', name_en: 'Debuff Success Down', name_jp: '弱体成功率DOWN', category: 'befoulment', stat: 'debuff_success', polarity: -1, suffix: '%', base_min: -16, base_max: -6 },
+  { slug: 'befoul_ability_dmg_down', name_en: 'Ability DMG Down', name_jp: 'アビリティダメージDOWN', category: 'befoulment', stat: 'ability_dmg', polarity: -1, suffix: '%', base_min: -50, base_max: -50 },
+])
+```
+
+---
+
+## Model Changes
+
+### WeaponStatModifier Model
+
+```ruby
+# app/models/weapon_stat_modifier.rb
+class WeaponStatModifier < ApplicationRecord
+  validates :slug, presence: true, uniqueness: true
+  validates :name_en, presence: true
+  validates :category, presence: true, inclusion: { in: %w[ax befoulment] }
+  validates :polarity, inclusion: { in: [-1, 1] }
+
+  scope :ax_skills, -> { where(category: 'ax') }
+  scope :befoulments, -> { where(category: 'befoulment') }
+
+  def self.find_by_game_skill_id(id)
+    find_by(game_skill_id: id.to_i)
+  end
+end
+```
+
+### CollectionWeapon Changes
+
+```ruby
+# app/models/collection_weapon.rb
+
+# Replace old integer references with proper associations
+belongs_to :ax_modifier1, class_name: 'WeaponStatModifier', optional: true
+belongs_to :ax_modifier2, class_name: 'WeaponStatModifier', optional: true
+belongs_to :befoulment_modifier, class_name: 'WeaponStatModifier', optional: true
+
+validates :exorcism_level, numericality: {
+  only_integer: true,
+  greater_than_or_equal_to: 0,
+  less_than_or_equal_to: 5
+}, allow_nil: true
+
+validate :validate_ax_skills
+validate :validate_befoulment_fields
+
+def validate_ax_skills
+  # AX skill 1: must have both modifier and strength
+  if (ax_modifier1.present? && ax_strength1.blank?) ||
+     (ax_modifier1.blank? && ax_strength1.present?)
+    errors.add(:base, "AX skill 1 must have both modifier and strength")
+  end
+
+  # AX skill 2: must have both modifier and strength
+  if (ax_modifier2.present? && ax_strength2.blank?) ||
+     (ax_modifier2.blank? && ax_strength2.present?)
+    errors.add(:base, "AX skill 2 must have both modifier and strength")
+  end
+
+  # Validate category is 'ax'
+  if ax_modifier1.present? && ax_modifier1.category != 'ax'
+    errors.add(:ax_modifier1, "must be an AX skill modifier")
+  end
+  if ax_modifier2.present? && ax_modifier2.category != 'ax'
+    errors.add(:ax_modifier2, "must be an AX skill modifier")
+  end
+end
+
+def validate_befoulment_fields
+  if (befoulment_modifier.present? && befoulment_strength.blank?) ||
+     (befoulment_modifier.blank? && befoulment_strength.present?)
+    errors.add(:base, "Befoulment must have both modifier and strength")
+  end
+
+  # Validate category is 'befoulment'
+  if befoulment_modifier.present? && befoulment_modifier.category != 'befoulment'
+    errors.add(:befoulment_modifier, "must be a befoulment modifier")
+  end
+end
+```
+
+### GridWeapon Changes
+
+```ruby
+# app/models/grid_weapon.rb
+
+# Same associations as CollectionWeapon
+belongs_to :ax_modifier1, class_name: 'WeaponStatModifier', optional: true
+belongs_to :ax_modifier2, class_name: 'WeaponStatModifier', optional: true
+belongs_to :befoulment_modifier, class_name: 'WeaponStatModifier', optional: true
+
+# Same validations as CollectionWeapon
+```
+
+- Update `sync_from_collection!` to include befoulment fields
+- Update `out_of_sync?` to check befoulment fields
+- Update Amoeba config to nullify befoulment fields on copy
+
+---
+
+## API Changes
+
+### Blueprint Serialization
+
+```ruby
+# collection_weapon_blueprint.rb
+
+# AX skills - now with full modifier object
+field :ax, if: ->(_, obj, _) { obj.ax_modifier1.present? } do |obj|
+  skills = []
+  if obj.ax_modifier1.present?
+    skills << {
+      modifier: WeaponStatModifierBlueprint.render_as_hash(obj.ax_modifier1),
+      strength: obj.ax_strength1
+    }
+  end
+  if obj.ax_modifier2.present?
+    skills << {
+      modifier: WeaponStatModifierBlueprint.render_as_hash(obj.ax_modifier2),
+      strength: obj.ax_strength2
+    }
+  end
+  skills
+end
+
+# Befoulment - with full modifier object
+field :befoulment, if: ->(_, obj, _) { obj.befoulment_modifier.present? } do |obj|
+  {
+    modifier: WeaponStatModifierBlueprint.render_as_hash(obj.befoulment_modifier),
+    strength: obj.befoulment_strength,
+    exorcism_level: obj.exorcism_level
+  }
+end
+
+# grid_weapon_blueprint.rb - similar
+```
+
+### WeaponStatModifierBlueprint
+
+```ruby
+# app/blueprints/api/v1/weapon_stat_modifier_blueprint.rb
+class Api::V1::WeaponStatModifierBlueprint < Blueprinter::Base
+  identifier :id
+  fields :slug, :name_en, :name_jp, :category, :stat, :polarity, :suffix
+end
+```
+
+### New Endpoint: GET /weapon_stat_modifiers
+
+Return all weapon stat modifiers for frontend reference:
+
+```ruby
+# app/controllers/api/v1/weapon_stat_modifiers_controller.rb
+def index
+  @modifiers = WeaponStatModifier.all
+  render json: WeaponStatModifierBlueprint.render(@modifiers, root: :weapon_stat_modifiers)
+end
+```
+
+### Controller Params
+
+Update `weapon_params` in both controllers:
+```ruby
+# Replace :ax_modifier1, :ax_modifier2 with FK versions
+:ax_modifier1_id, :ax_strength1, :ax_modifier2_id, :ax_strength2,
+:befoulment_modifier_id, :befoulment_strength, :exorcism_level
+```
+
+---
+
+## Import Service
+
+### Game JSON Structure
+
+**Odiant weapon (with befoulment):**
+```json
+{
+  "augment_skill_info": [[{ "skill_id": 2880, "effect_value": "25", "show_value": "-25%" }]],
+  "odiant": {
+    "is_odiant_weapon": true,
+    "exorcision_level": 1,
+    "max_exorcision_level": 5
+  }
+}
+```
+
+**Regular weapon (with AX skills):**
+```json
+{
+  "augment_skill_info": [[
+    { "skill_id": 1589, "effect_value": "3", "show_value": "+3%" },
+    { "skill_id": 1719, "effect_value": "1_2000", "show_value": "+3" }
+  ]],
+  "odiant": {
+    "is_odiant_weapon": false,
+    "exorcision_level": 0
+  }
+}
+```
+
+**Key insight:** Same `augment_skill_info` structure, differentiated by `is_odiant_weapon`:
+- `true` → parse as befoulment (skill_id 2880+)
+- `false` → parse as AX skills (skill_id 1588-1722)
+
+### WeaponImportService Updates
+
+Add a cache for WeaponStatModifier lookups:
+
+```ruby
+def initialize(user, game_data, options = {})
+  # ... existing code ...
+  @modifier_cache = {}  # Cache for WeaponStatModifier lookups
+end
+
+def build_collection_weapon_attrs(item, weapon)
+  param = item['param'] || {}
+
+  attrs = {
+    weapon: weapon,
+    game_id: param['id'].to_s,
+    # ... existing attrs ...
+  }
+
+  # Check if this is an Odiant (befoulment) weapon
+  odiant = param['odiant']
+  if odiant && odiant['is_odiant_weapon'] == true
+    # Parse befoulment from augment_skill_info
+    befoulment = parse_befoulment(param['augment_skill_info'])
+    if befoulment
+      attrs[:befoulment_modifier_id] = befoulment[:modifier_id]
+      attrs[:befoulment_strength] = befoulment[:strength]
+    end
+    attrs[:exorcism_level] = odiant['exorcision_level'].to_i
+  else
+    # Regular weapon - parse AX skills
+    ax_attrs = parse_ax_skills(param['augment_skill_info'])
+    attrs.merge!(ax_attrs) if ax_attrs
+  end
+
+  # ... rest of existing code (awakening, etc) ...
+  attrs
+end
+
+# Updated to return FK id instead of raw game_skill_id
+def parse_ax_skills(augment_skill_info)
+  return nil if augment_skill_info.blank? || !augment_skill_info.is_a?(Array)
+
+  skills = augment_skill_info.first
+  return nil if skills.blank? || !skills.is_a?(Array)
+
+  attrs = {}
+
+  # First AX skill
+  if skills[0].is_a?(Hash)
+    ax1 = parse_single_ax_skill(skills[0])
+    if ax1
+      attrs[:ax_modifier1_id] = ax1[:modifier_id]
+      attrs[:ax_strength1] = ax1[:strength]
+    end
+  end
+
+  # Second AX skill
+  if skills[1].is_a?(Hash)
+    ax2 = parse_single_ax_skill(skills[1])
+    if ax2
+      attrs[:ax_modifier2_id] = ax2[:modifier_id]
+      attrs[:ax_strength2] = ax2[:strength]
+    end
+  end
+
+  attrs.empty? ? nil : attrs
+end
+
+def parse_single_ax_skill(skill)
+  return nil unless skill['skill_id'].present?
+
+  game_skill_id = skill['skill_id'].to_i
+  modifier = find_modifier_by_game_skill_id(game_skill_id)
+  return nil unless modifier
+
+  strength = parse_ax_strength(skill['effect_value'], skill['show_value'])
+  return nil unless strength
+
+  { modifier_id: modifier.id, strength: strength }
+end
+
+def parse_befoulment(augment_skill_info)
+  return nil if augment_skill_info.blank? || !augment_skill_info.is_a?(Array)
+
+  skills = augment_skill_info.first
+  return nil if skills.blank? || !skills.is_a?(Array)
+
+  skill = skills.first
+  return nil unless skill.is_a?(Hash) && skill['skill_id'].present?
+
+  game_skill_id = skill['skill_id'].to_i
+  modifier = find_modifier_by_game_skill_id(game_skill_id)
+  return nil unless modifier
+
+  {
+    modifier_id: modifier.id,
+    strength: parse_befoulment_strength(skill['effect_value'], skill['show_value'])
+  }
+end
+
+def find_modifier_by_game_skill_id(game_skill_id)
+  @modifier_cache[game_skill_id] ||= WeaponStatModifier.find_by(game_skill_id: game_skill_id)
+end
+
+def parse_befoulment_strength(effect_value, show_value)
+  # show_value has the sign: "-25%"
+  # effect_value is unsigned: "25"
+  if show_value.present?
+    show_value.to_s.gsub('%', '').to_f
+  elsif effect_value.present?
+    -effect_value.to_f
+  end
+end
+```
+
+**Note:** Unknown `game_skill_id` values will be skipped (modifier not found). This is acceptable - we can add new modifiers to the seed data as we discover them.
+
+---
+
+## Files to Create/Modify
+
+| File | Action |
+|------|--------|
+| **Migrations** | |
+| `db/migrate/xxx_create_weapon_stat_modifiers.rb` | Create - new reference table |
+| `db/migrate/xxx_refactor_ax_and_add_befoulments.rb` | Create - replace ax_modifier integers with FKs, add befoulment FKs |
+| `db/migrate/xxx_replace_has_ax_skills_with_augment_type.rb` | Create - enum migration with data migration |
+| `db/data/xxx_migrate_ax_modifiers_to_fk.rb` | Create - data migration to convert existing ax_modifier values to FK references |
+| **Models** | |
+| `app/models/weapon_stat_modifier.rb` | Create |
+| `app/models/collection_weapon.rb` | Modify - add befoulment validation |
+| `app/models/grid_weapon.rb` | Modify - add befoulment fields, sync |
+| `app/models/weapon_series.rb` | Modify - replace has_ax_skills with augment_type enum |
+| **Blueprints** | |
+| `app/blueprints/api/v1/weapon_stat_modifier_blueprint.rb` | Create |
+| `app/blueprints/api/v1/collection_weapon_blueprint.rb` | Modify - add befoulment serialization |
+| `app/blueprints/api/v1/grid_weapon_blueprint.rb` | Modify - add befoulment serialization |
+| `app/blueprints/api/v1/weapon_series_blueprint.rb` | Modify - replace has_ax_skills with augment_type |
+| `app/blueprints/api/v1/weapon_blueprint.rb` | Modify - update series.has_ax_skills reference |
+| **Controllers** | |
+| `app/controllers/api/v1/weapon_stat_modifiers_controller.rb` | Create |
+| `app/controllers/api/v1/collection_weapons_controller.rb` | Modify - permit befoulment params |
+| `app/controllers/api/v1/grid_weapons_controller.rb` | Modify - permit befoulment params |
+| `app/controllers/api/v1/weapon_series_controller.rb` | Modify - permit augment_type instead of has_ax_skills |
+| **Services & Seeds** | |
+| `app/services/weapon_import_service.rb` | Modify - parse befoulments |
+| `db/seeds/weapon_stat_modifiers.rb` | Create |
+| **Config & Tests** | |
+| `config/routes.rb` | Modify - add weapon_stat_modifiers route |
+| `spec/factories/weapon_series.rb` | Modify - replace has_ax_skills with augment_type |
+
+---
+
+## API Breaking Changes
+
+### 1. WeaponSeries: `has_ax_skills` → `augment_type`
+
+**Before:**
+```json
+{ "has_ax_skills": true }
+```
+
+**After:**
+```json
+{ "augment_type": "ax" }  // or "befoulment" or "none"
+```
+
+Frontend: `augment_type === 'ax'` instead of `has_ax_skills === true`.
+
+### 2. Collection/GridWeapon: AX skill structure changed
+
+**Before:**
+```json
+{
+  "ax_modifier1": 1589,
+  "ax_strength1": 3.0,
+  "ax_modifier2": 1719,
+  "ax_strength2": 2000
+}
+```
+
+**After:**
+```json
+{
+  "ax": [
+    {
+      "modifier": { "id": 1, "slug": "ax_atk", "name_en": "ATK Up", "category": "ax", ... },
+      "strength": 3.0
+    },
+    {
+      "modifier": { "id": 5, "slug": "ax_ability_dmg", "name_en": "Ability DMG Up", "category": "ax", ... },
+      "strength": 2000
+    }
+  ]
+}
+```
+
+Frontend: Access via `weapon.ax[0].modifier.slug` instead of `weapon.ax_modifier1`.
+
+---
+
+## Implementation Considerations
+
+### Migration Order
+
+Migrations must be deployed in this order:
+
+1. `create_weapon_stat_modifiers` - Create table + seed data
+2. `add_ax_and_befoulment_fk_columns` - Add new FK columns (keep old integer columns)
+3. `migrate_ax_modifiers_to_fk` - Data migration: lookup existing values → FK refs
+4. `remove_old_ax_modifier_columns` - Remove old integer columns
+5. `replace_has_ax_skills_with_augment_type` - WeaponSeries enum change
+
+### GridWeapon Amoeba Config
+
+Update nullify list for party cloning:
+
+```ruby
+amoeba do
+  nullify :ax_modifier1_id
+  nullify :ax_modifier2_id
+  nullify :ax_strength1
+  nullify :ax_strength2
+  nullify :befoulment_modifier_id
+  nullify :befoulment_strength
+  nullify :exorcism_level
+end
+```
+
+### Unknown Skill ID Logging
+
+When import encounters unknown `game_skill_id`, log with icon image for discovery:
+
+```ruby
+Rails.logger.warn(
+  "[WeaponImportService] Unknown augment skill_id=#{game_skill_id} " \
+  "icon=#{skill['augment_skill_icon_image']}"
+)
+```
+
+### Database Indexes
+
+Add index on `weapon_stat_modifiers.game_skill_id` for fast import lookups:
+
+```ruby
+add_index :weapon_stat_modifiers, :game_skill_id, unique: true
+```
+
+### Coordinated Release
+
+Frontend and backend releases will be coordinated. No backwards compatibility layer needed.
+
+---
+
+## Next Steps
+
+1. ✅ **Game JSON samples** - received for both Odiant and regular weapons
+2. **Identify Odiant weapon series** in database (set `augment_type: :befoulment`)
+3. **Discover remaining game_skill_ids** for other befoulment types (we know 2880 = DEF Down)
+4. **Verify AX skill IDs** match between AX_MAPPING and game data
+
+## Known Skill IDs
+
+### AX Skills (Complete)
+
+| skill_id | Stat | Name (EN) | Name (JP) | Suffix |
+|----------|------|-----------|-----------|--------|
+| 1588 | hp | HP | HP | % |
+| 1589 | atk | ATK | 攻撃 | % |
+| 1590 | def | DEF | 防御 | % |
+| 1591 | ca_dmg | C.A. DMG | 奥義ダメ | % |
+| 1592 | multiattack | Multiattack Rate | 連撃率 | % |
+| 1593 | debuff_res | Debuff Resistance | 弱体耐性 | % |
+| 1594 | ele_atk | Elemental ATK | 全属性攻撃力 | % |
+| 1595 | healing | Healing | 回復性能 | % |
+| 1596 | da | Double Attack Rate | DA確率 | % |
+| 1597 | ta | Triple Attack Rate | TA確率 | % |
+| 1599 | ca_cap | C.A. DMG Cap | 奥義上限 | % |
+| 1600 | stamina | Stamina | 渾身 | - |
+| 1601 | enmity | Enmity | 背水 | - |
+| 1719 | skill_supp | Supplemental Skill DMG | アビ与ダメ上昇 | - |
+| 1720 | ca_supp | Supplemental C.A. DMG | 奥義与ダメ上昇 | - |
+| 1721 | ele_dmg_red | Elemental DMG Reduction | 属性ダメ軽減 | % |
+| 1722 | na_cap | Normal ATK DMG Cap | 通常ダメ上限 | % |
+| 1837 | exp | EXP Gain | EXP UP | % |
+| 1838 | rupie | Rupie Gain | 獲得ルピ | % |
+
+### Befoulments (Partial - more to discover)
+
+| skill_id | Stat | Name (EN) | Name (JP) |
+|----------|------|-----------|-----------|
+| 2880 | def | DEF Down | 防御力DOWN |
+| ? | atk | ATK Down | 攻撃力DOWN |
+| ? | da_ta | DA/TA Down | 連撃率DOWN |
+| ? | ca_dmg | CA DMG Down | 奥義ダメージDOWN |
+| ? | dot | Damage Over Time | 毎ターンダメージ |
+| ? | hp | Max HP Down | 最大HP減少 |
+| ? | debuff_success | Debuff Success Down | 弱体成功率DOWN |
+| ? | ability_dmg | Ability DMG Down | アビリティダメージDOWN |
+
+(Befoulment skill_ids will be discovered as users import Odiant weapons)