add related characters endpoint

app/controllers/api/v1/characters_controller.rb

@@ -11,6 +11,14 @@ module Api
         render json: CharacterBlueprint.render(@character, view: :full)
       end
 
+      def related
+        return render json: [] unless @character.character_id
+
+        related = Character.where(character_id: @character.character_id)
+                           .where.not(id: @character.id)
+        render json: CharacterBlueprint.render(related)
+      end
+
       private
 
       def set

config/routes.rb

@@ -54,6 +54,8 @@ Rails.application.routes.draw do
     get 'jobs/:id/skills', to: 'job_skills#job'
     get 'jobs/:id/accessories', to: 'job_accessories#job'
 
+    get 'characters/:id/related', to: 'characters#related'
+
     get 'guidebooks', to: 'guidebooks#all'
 
     get 'raids', to: 'raids#all'