diff --git a/src/assets/icons/loader-2.svg b/src/assets/icons/loader-2.svg
new file mode 100644
index 00000000..a55230b6
--- /dev/null
+++ b/src/assets/icons/loader-2.svg
@@ -0,0 +1,3 @@
+<svg width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" xmlns="http://www.w3.org/2000/svg">
+<path d="M21 12a9 9 0 1 1-6.219-8.56"/>
+</svg>
diff --git a/src/lib/api/adapters/grid.adapter.ts b/src/lib/api/adapters/grid.adapter.ts
index 0e8ed984..c1d136bb 100644
--- a/src/lib/api/adapters/grid.adapter.ts
+++ b/src/lib/api/adapters/grid.adapter.ts
@@ -10,8 +10,10 @@
 import { BaseAdapter } from './base.adapter'
 import type { AdapterOptions } from './types'
 import type { GridWeapon, GridCharacter, GridSummon } from '$lib/types/api/party'
+import type { Character, Weapon } from '$lib/types/api/entities'
 import { DEFAULT_ADAPTER_CONFIG } from './config'
 import { validateGridWeapon, validateGridCharacter, validateGridSummon } from '$lib/utils/gridValidation'
+import { isConflictResponse } from '$lib/types/api/conflict'
 
 // GridWeapon, GridCharacter, and GridSummon types are imported from types/api/party
 // Re-export for test files and consumers
@@ -88,6 +90,24 @@ export interface ResolveConflictParams {
 	conflictingIds: string[]
 }
 
+/**
+ * Character conflict response from API
+ */
+export interface CharacterConflictResponse {
+	position: number
+	conflicts: GridCharacter[]
+	incoming: Character
+}
+
+/**
+ * Weapon conflict response from API
+ */
+export interface WeaponConflictResponse {
+	position: number
+	conflicts: GridWeapon[]
+	incoming: Weapon
+}
+
 /**
  * Grid adapter for managing user's grid item instances
  */
@@ -97,16 +117,23 @@ export class GridAdapter extends BaseAdapter {
 
 	/**
 	 * Creates a new grid weapon instance
+	 * Returns either a GridWeapon on success, or a WeaponConflictResponse if conflicts are detected
 	 */
-    async createWeapon(params: CreateGridWeaponParams, headers?: Record<string, string>): Promise<GridWeapon> {
-        const response = await this.request<{ gridWeapon: GridWeapon }>('/grid_weapons', {
+    async createWeapon(params: CreateGridWeaponParams, headers?: Record<string, string>): Promise<GridWeapon | WeaponConflictResponse> {
+        const response = await this.request<{ gridWeapon: GridWeapon } | WeaponConflictResponse>('/grid_weapons', {
             method: 'POST',
             body: { weapon: params },
             headers
         })
 
-        // Validate and normalize response
-        const validated = validateGridWeapon(response.gridWeapon)
+        // Check if this is a conflict response
+        if (isConflictResponse(response)) {
+            return response as WeaponConflictResponse
+        }
+
+        // Normal success response - validate and normalize
+        const gridWeaponResponse = response as { gridWeapon: GridWeapon }
+        const validated = validateGridWeapon(gridWeaponResponse.gridWeapon)
         if (!validated) {
             throw new Error('API returned incomplete GridWeapon data')
         }
@@ -208,16 +235,23 @@ export class GridAdapter extends BaseAdapter {
 
 	/**
 	 * Creates a new grid character instance
+	 * Returns either a GridCharacter on success, or a CharacterConflictResponse if conflicts are detected
 	 */
-    async createCharacter(params: CreateGridCharacterParams, headers?: Record<string, string>): Promise<GridCharacter> {
-        const response = await this.request<{ gridCharacter: GridCharacter }>('/grid_characters', {
+    async createCharacter(params: CreateGridCharacterParams, headers?: Record<string, string>): Promise<GridCharacter | CharacterConflictResponse> {
+        const response = await this.request<{ gridCharacter: GridCharacter } | CharacterConflictResponse>('/grid_characters', {
             method: 'POST',
             body: { character: params },
             headers
         })
 
-        // Validate and normalize response
-        const validated = validateGridCharacter(response.gridCharacter)
+        // Check if this is a conflict response
+        if (isConflictResponse(response)) {
+            return response as CharacterConflictResponse
+        }
+
+        // Normal success response - validate and normalize
+        const gridCharacterResponse = response as { gridCharacter: GridCharacter }
+        const validated = validateGridCharacter(gridCharacterResponse.gridCharacter)
         if (!validated) {
             throw new Error('API returned incomplete GridCharacter data')
         }
diff --git a/src/lib/components/dialogs/ConflictDialog.module.scss b/src/lib/components/dialogs/ConflictDialog.module.scss
new file mode 100644
index 00000000..3a9a6eda
--- /dev/null
+++ b/src/lib/components/dialogs/ConflictDialog.module.scss
@@ -0,0 +1,83 @@
+/**
+ * ConflictDialog Styles
+ *
+ * Layout: [Conflicting Items] → [Incoming Item]
+ */
+
+@use '$src/themes/spacing' as *;
+@use '$src/themes/typography' as *;
+
+$item-diameter: 10rem;
+
+.content {
+	display: flex;
+	flex-direction: column;
+	gap: $unit-3x;
+}
+
+.message {
+	font-size: $font-regular;
+	line-height: 1.5;
+	color: var(--text-primary);
+
+	:global(strong) {
+		font-weight: $bold;
+	}
+}
+
+.diagram {
+	display: grid;
+	grid-template-columns: 1fr auto 1fr;
+	align-items: center;
+	gap: $unit-2x;
+}
+
+.conflicts {
+	display: flex;
+	flex-direction: column;
+	align-items: center;
+	gap: $unit-2x;
+	list-style: none;
+	padding: 0;
+	margin: 0;
+}
+
+.item {
+	display: flex;
+	flex-direction: column;
+	align-items: center;
+	gap: $unit;
+	text-align: center;
+	width: $item-diameter;
+	font-weight: $medium;
+	font-size: $font-small;
+
+	img {
+		border-radius: $unit;
+		width: $item-diameter;
+		height: auto;
+		aspect-ratio: 1;
+		object-fit: cover;
+	}
+
+	span {
+		line-height: 1.3;
+		color: var(--text-primary);
+	}
+}
+
+.arrow {
+	display: flex;
+	align-items: center;
+	justify-content: center;
+	font-size: 3rem;
+	color: var(--text-tertiary);
+	height: $item-diameter;
+	padding: 0 $unit;
+}
+
+.incoming {
+	display: flex;
+	justify-content: center;
+	width: 100%;
+}
diff --git a/src/lib/components/dialogs/ConflictDialog.svelte b/src/lib/components/dialogs/ConflictDialog.svelte
new file mode 100644
index 00000000..3489b97a
--- /dev/null
+++ b/src/lib/components/dialogs/ConflictDialog.svelte
@@ -0,0 +1,239 @@
+<!--
+  ConflictDialog Component
+
+  A unified dialog for handling character and weapon conflicts when adding
+  units to a party that would violate uniqueness constraints.
+
+  Usage:
+  ```svelte
+  <ConflictDialog
+    bind:open={conflictDialogOpen}
+    conflict={conflictData}
+    partyId={party.id}
+    partyShortcode={party.shortcode}
+    onResolve={() => { conflictData = null }}
+    onCancel={() => { conflictData = null }}
+  />
+  ```
+-->
+<script lang="ts">
+	import Dialog from '$lib/components/ui/Dialog.svelte'
+	import Button from '$lib/components/ui/Button.svelte'
+	import type { ConflictData } from '$lib/types/api/conflict'
+	import type { GridCharacter, GridWeapon } from '$lib/types/api/party'
+	import type { Character, Weapon } from '$lib/types/api/entities'
+	import { useResolveCharacterConflict, useResolveWeaponConflict } from '$lib/api/mutations/grid.mutations'
+	import { getCharacterImageWithPose, getWeaponImage } from '$lib/utils/images'
+	import { getWeaponSeriesSlug, isOpusDraconicSeries } from '$lib/utils/weaponSeries'
+	import { getLocale } from '$lib/paraglide/runtime.js'
+	import * as m from '$lib/paraglide/messages'
+
+	import styles from './ConflictDialog.module.scss'
+
+	interface Props {
+		/** Controls dialog visibility */
+		open: boolean
+		/** Conflict data from API response */
+		conflict: ConflictData | null
+		/** Party ID for resolve request */
+		partyId: string
+		/** Party shortcode for cache invalidation */
+		partyShortcode: string
+		/** Callback when conflict is resolved */
+		onResolve?: () => void
+		/** Callback when dialog is cancelled */
+		onCancel?: () => void
+	}
+
+	let {
+		open = $bindable(false),
+		conflict,
+		partyId,
+		partyShortcode,
+		onResolve,
+		onCancel
+	}: Props = $props()
+
+	// Mutations for resolving conflicts
+	const resolveCharacterMutation = useResolveCharacterConflict()
+	const resolveWeaponMutation = useResolveWeaponConflict()
+
+	// Get current locale for name display
+	const locale = $derived(getLocale() as 'en' | 'ja')
+
+	// Loading state - use mutation.current in Svelte 5
+	let isLoading = $state(false)
+
+	// Generate conflict message based on type
+	const conflictMessage = $derived.by(() => {
+		if (!conflict) return ''
+
+		if (conflict.type === 'character') {
+			return m.conflict_character_message()
+		}
+
+		// Weapon conflict - check if it's Opus/Draconic
+		const weapon = conflict.incoming
+		if (isOpusDraconicSeries(weapon.series)) {
+			return m.conflict_weapon_opus_draconic()
+		}
+
+		// Get series name for message
+		const seriesSlug = getWeaponSeriesSlug(weapon.series)
+
+		// Use the series slug directly for now - proper i18n can be added later
+		const seriesName = seriesSlug?.replace(/_/g, ' ').replace(/\b\w/g, l => l.toUpperCase()) || 'Unknown'
+
+		return m.conflict_weapon_series({ series: seriesName })
+	})
+
+	/**
+	 * Handle confirm button click - resolve the conflict
+	 */
+	async function handleResolve() {
+		if (!conflict) return
+
+		const resolveParams = {
+			partyId,
+			partyShortcode,
+			incomingId: conflict.incoming.id,
+			position: conflict.position,
+			conflictingIds: conflict.conflicts.map((c) => c.id)
+		}
+
+		isLoading = true
+		try {
+			if (conflict.type === 'character') {
+				await resolveCharacterMutation.mutateAsync(resolveParams)
+			} else {
+				await resolveWeaponMutation.mutateAsync(resolveParams)
+			}
+
+			open = false
+			onResolve?.()
+		} catch (error) {
+			console.error('[ConflictDialog] Failed to resolve conflict:', error)
+			// Error will be handled by mutation's error state
+		} finally {
+			isLoading = false
+		}
+	}
+
+	/**
+	 * Handle cancel button click
+	 */
+	function handleCancel() {
+		open = false
+		onCancel?.()
+	}
+
+	/**
+	 * Handle dialog open change (e.g., clicking overlay or X button)
+	 */
+	function handleOpenChange(newOpen: boolean) {
+		if (!newOpen) {
+			handleCancel()
+		}
+	}
+
+	/**
+	 * Get character image URL with proper pose
+	 */
+	function getCharacterUrl(gridChar: GridCharacter): string {
+		return getCharacterImageWithPose(
+			gridChar.character.granblueId,
+			'square',
+			gridChar.uncapLevel,
+			gridChar.transcendenceStep
+		)
+	}
+
+	/**
+	 * Get incoming character image URL (default pose)
+	 */
+	function getIncomingCharacterUrl(character: Character): string {
+		return getCharacterImageWithPose(character.granblueId, 'square', 0, 0)
+	}
+
+	/**
+	 * Get weapon image URL
+	 */
+	function getWeaponUrl(gridWeapon: GridWeapon): string {
+		return getWeaponImage(gridWeapon.weapon.granblueId, 'square')
+	}
+
+	/**
+	 * Get incoming weapon image URL
+	 */
+	function getIncomingWeaponUrl(weapon: Weapon): string {
+		return getWeaponImage(weapon.granblueId, 'square')
+	}
+</script>
+
+<Dialog bind:open onOpenChange={handleOpenChange} title={m.conflict_title()}>
+	{#if conflict}
+		<div class={styles.content}>
+			<p class={styles.message}>{conflictMessage}</p>
+
+			<div class={styles.diagram}>
+				<!-- Conflicting items (left side) -->
+				<ul class={styles.conflicts}>
+					{#if conflict.type === 'character'}
+						{#each conflict.conflicts as gridChar (gridChar.id)}
+							<li class={styles.item}>
+								<img
+									src={getCharacterUrl(gridChar)}
+									alt={gridChar.character.name[locale]}
+								/>
+								<span>{gridChar.character.name[locale]}</span>
+							</li>
+						{/each}
+					{:else}
+						{#each conflict.conflicts as gridWeapon (gridWeapon.id)}
+							<li class={styles.item}>
+								<img
+									src={getWeaponUrl(gridWeapon)}
+									alt={gridWeapon.weapon.name[locale]}
+								/>
+								<span>{gridWeapon.weapon.name[locale]}</span>
+							</li>
+						{/each}
+					{/if}
+				</ul>
+
+				<!-- Arrow -->
+				<span class={styles.arrow}>&rarr;</span>
+
+				<!-- Incoming item (right side) -->
+				<div class={styles.incoming}>
+					{#if conflict.type === 'character'}
+						<div class={styles.item}>
+							<img
+								src={getIncomingCharacterUrl(conflict.incoming)}
+								alt={conflict.incoming.name[locale]}
+							/>
+							<span>{conflict.incoming.name[locale]}</span>
+						</div>
+					{:else}
+						<div class={styles.item}>
+							<img
+								src={getIncomingWeaponUrl(conflict.incoming)}
+								alt={conflict.incoming.name[locale]}
+							/>
+							<span>{conflict.incoming.name[locale]}</span>
+						</div>
+					{/if}
+				</div>
+			</div>
+		</div>
+	{/if}
+
+	{#snippet footer()}
+		<Button variant="ghost" onclick={handleCancel} disabled={isLoading}>
+			{m.conflict_cancel()}
+		</Button>
+		<Button variant="primary" onclick={handleResolve} disabled={isLoading}>
+			{m.conflict_confirm()}
+		</Button>
+	{/snippet}
+</Dialog>
diff --git a/src/lib/types/api/conflict.ts b/src/lib/types/api/conflict.ts
new file mode 100644
index 00000000..835c91bc
--- /dev/null
+++ b/src/lib/types/api/conflict.ts
@@ -0,0 +1,92 @@
+/**
+ * Conflict Types
+ *
+ * Type definitions for conflict detection and resolution when adding
+ * characters or weapons to a party that would violate uniqueness constraints.
+ *
+ * @module types/api/conflict
+ */
+
+import type { Character, Weapon } from './entities'
+import type { GridCharacter, GridWeapon } from './party'
+
+/**
+ * Types of units that can have conflicts
+ */
+export type ConflictType = 'character' | 'weapon'
+
+/**
+ * Conflict data when adding a character that already exists in the party
+ */
+export interface CharacterConflictData {
+	type: 'character'
+	position: number
+	conflicts: GridCharacter[]
+	incoming: Character
+}
+
+/**
+ * Conflict data when adding a weapon that violates series constraints
+ */
+export interface WeaponConflictData {
+	type: 'weapon'
+	position: number
+	conflicts: GridWeapon[]
+	incoming: Weapon
+}
+
+/**
+ * Union type for all conflict data
+ */
+export type ConflictData = CharacterConflictData | WeaponConflictData
+
+/**
+ * Raw conflict response from API (before adding type discriminator)
+ */
+export interface RawConflictResponse {
+	position: number
+	conflicts: unknown[]
+	incoming: unknown
+}
+
+/**
+ * Type guard to check if an API response is a conflict response.
+ * Conflict responses have `conflicts`, `incoming`, and `position` properties.
+ *
+ * @param data - The API response data to check
+ * @returns True if the response is a conflict response
+ */
+export function isConflictResponse(data: unknown): data is RawConflictResponse {
+	return (
+		data !== null &&
+		typeof data === 'object' &&
+		'conflicts' in data &&
+		'incoming' in data &&
+		'position' in data &&
+		Array.isArray((data as RawConflictResponse).conflicts)
+	)
+}
+
+/**
+ * Creates typed ConflictData from a raw API conflict response.
+ *
+ * @param raw - The raw conflict response from the API
+ * @param type - The type of conflict ('character' or 'weapon')
+ * @returns Typed ConflictData ready for use in ConflictDialog
+ */
+export function createConflictData(raw: RawConflictResponse, type: ConflictType): ConflictData {
+	if (type === 'character') {
+		return {
+			type: 'character',
+			position: raw.position,
+			conflicts: raw.conflicts as GridCharacter[],
+			incoming: raw.incoming as Character
+		}
+	}
+	return {
+		type: 'weapon',
+		position: raw.position,
+		conflicts: raw.conflicts as GridWeapon[],
+		incoming: raw.incoming as Weapon
+	}
+}