diff --git a/backend/app/controllers/nico_tags_controller.rb b/backend/app/controllers/nico_tags_controller.rb
index 973d70f..f0e33a4 100644
--- a/backend/app/controllers/nico_tags_controller.rb
+++ b/backend/app/controllers/nico_tags_controller.rb
@@ -38,7 +38,7 @@ class NicoTagsController < ApplicationController
     return head :bad_request if linked_tags.any? { |t| t.nico? }
 
     ApplicationRecord.transaction do
-      record_tag_snapshots!(linked_tags, created_by_user: current_user)
+      TagVersioning.record_tag_snapshots!(linked_tags, created_by_user: current_user)
 
       tag.linked_tags = linked_tags
       tag.save!
@@ -48,13 +48,4 @@ class NicoTagsController < ApplicationController
 
     render json: tag.linked_tags.map { |t| TagRepr.base(t) }, status: :ok
   end
-
-  private
-
-  def record_tag_snapshots! tags, created_by_user:
-    tags.each do |tag|
-      event_type = tag.tag_versions.exists? ? :update : :create
-      TagVersionRecorder.record!(tag:, event_type:, created_by_user:)
-    end
-  end
 end
diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index 03e2d8a..300392a 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -131,7 +131,7 @@ class PostsController < ApplicationController
     ApplicationRecord.transaction do
       post.save!
       tags = Tag.normalise_tags(tag_names)
-      record_tag_snapshots!(tags, created_by_user: current_user)
+      TagVersioning.record_tag_snapshots!(tags, created_by_user: current_user)
 
       tags = Tag.expand_parent_tags(tags)
       sync_post_tags!(post, tags)
@@ -175,10 +175,10 @@ class PostsController < ApplicationController
     ApplicationRecord.transaction do
       post.update!(title:, original_created_from:, original_created_before:)
 
-      normalised_tag = Tag.normalise_tags(tag_names, with_tagme: false)
-      record_tag_snapshots(normalised_tags, create_by_user: current_user)
+      normalised_tags = Tag.normalise_tags(tag_names, with_tagme: false)
+      TagVersioning.record_tag_snapshots!(normalised_tags, created_by_user: current_user)
 
-      tags = post.tags.where(category: 'nico').to_a + normalised_tags
+      tags = post.tags.nico.to_a + normalised_tags
       tags = Tag.expand_parent_tags(tags)
       sync_post_tags!(post, tags)
       PostVersionRecorder.record!(post:, event_type: :update, created_by_user: current_user)
diff --git a/backend/app/controllers/tags_controller.rb b/backend/app/controllers/tags_controller.rb
index 71b7309..9b23fd1 100644
--- a/backend/app/controllers/tags_controller.rb
+++ b/backend/app/controllers/tags_controller.rb
@@ -218,21 +218,14 @@ class TagsController < ApplicationController
 
     tag = Tag.find(params[:id])
 
-    ApplicationRecord.transaction do
-      old_nico = tag.nico?
-
-      if category.present?
-        new_nico = category == 'nico'
-
-        if old_nico != new_nico
-          return render json: { error: 'ニコタグのカテゴリ変更はできません．' },
-                        status: :unprocessable_entity
-        end
-      end
+    if category.present? && tag.nico? != (category == 'nico')
+      return render json: { error: 'ニコタグのカテゴリ変更はできません．' },
+                    status: :unprocessable_entity
+    end
 
+    ApplicationRecord.transaction do
       tag.tag_name.update!(name:) if name.present?
       tag.update!(category:) if category.present?
-
       record_tag_version!(tag, event_type: :update, created_by_user: current_user)
     end
 
diff --git a/backend/app/models/nico_tag_version.rb b/backend/app/models/nico_tag_version.rb
new file mode 100644
index 0000000..b57252a
--- /dev/null
+++ b/backend/app/models/nico_tag_version.rb
@@ -0,0 +1,7 @@
+class NicoTagVersion < ApplicationRecord
+  include VersionRecord
+
+  belongs_to :tag
+
+  validates :name, presence: true
+end
diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index 8ac0f33..3730b1e 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -157,7 +157,6 @@ class Tag < ApplicationRecord
     target_tag => Tag
 
     affected_post_ids = Set.new
-    affected_tag_ids = Set.new
 
     Tag.transaction do
       Array(source_tags).compact.uniq.each do |source_tag|
@@ -181,7 +180,7 @@ class Tag < ApplicationRecord
         end
 
         source_tag.discard!
-        record_tag_discard!(source_tag, current_by_user: nil)
+        TagVersioning.record!(source_tag, event_type: :discard, created_by_user:)
 
         if source_tag.nico?
           source_tag_name.discard!
@@ -190,7 +189,7 @@ class Tag < ApplicationRecord
                                          updated_at: Time.current)
         end
 
-        record_tag_version!(target_tag, event_type: :update, created_by_user: nil)
+        TagVersioning.record!(target_tag, event_type: :update, created_by_user:)
       end
 
       Post.where(id: affected_post_ids.to_a).find_each do |post|
diff --git a/backend/app/models/tag_name.rb b/backend/app/models/tag_name.rb
index b118300..de79d10 100644
--- a/backend/app/models/tag_name.rb
+++ b/backend/app/models/tag_name.rb
@@ -1,8 +1,6 @@
 class TagName < ApplicationRecord
   include MyDiscard
 
-  default_scope -> { kept }
-
   has_one :tag
   has_one :wiki_page
 
diff --git a/backend/app/models/tag_version.rb b/backend/app/models/tag_version.rb
index c15933e..6ca5d0a 100644
--- a/backend/app/models/tag_version.rb
+++ b/backend/app/models/tag_version.rb
@@ -8,8 +8,7 @@ class TagVersion < ApplicationRecord
                     character: 'character',
                     general: 'general',
                     material: 'material',
-                    meta: 'meta',
-                    nico: 'nico' }, validate: true
+                    meta: 'meta' }, validate: true
 
   validates :name, presence: true
   validates :category, presence: true
diff --git a/backend/app/services/nico_tag_version_recorder.rb b/backend/app/services/nico_tag_version_recorder.rb
index 07a5c63..09f953e 100644
--- a/backend/app/services/nico_tag_version_recorder.rb
+++ b/backend/app/services/nico_tag_version_recorder.rb
@@ -12,5 +12,8 @@ class NicoTagVersionRecorder < VersionRecorder
   def version_class = NicoTagVersion
   def version_association = :nico_tag_versions
   def record_key = :tag
-  def snapshot_attributes = { name: @tag.name, linked_tags: @tag.snapshot_linked_tags.join(' ') }
+
+  def snapshot_attributes
+    { name: @record.name, linked_tags: @record.snapshot_linked_tags.join(' ') }
+  end
 end
diff --git a/backend/app/services/post_version_recorder.rb b/backend/app/services/post_version_recorder.rb
index 87e267e..589e6d8 100644
--- a/backend/app/services/post_version_recorder.rb
+++ b/backend/app/services/post_version_recorder.rb
@@ -1,4 +1,4 @@
-class PostVersionRecorder
+class PostVersionRecorder < VersionRecorder
   def self.record! post:, event_type:, created_by_user:
     new(post:, event_type:, created_by_user:).record!
   end
@@ -14,12 +14,12 @@ class PostVersionRecorder
   def record_key = :post
 
   def snapshot_attributes
-    { title: @post.title,
-      url: @post.url,
-      thumbnail_base: @post.thumbnail_base,
-      tags: @post.snapshot_tag_names.join(' '),
-      parent: @post.parent,
-      original_created_from: @post.original_created_from,
-      original_created_before: @post.original_created_before }
+    { title: @record.title,
+      url: @record.url,
+      thumbnail_base: @record.thumbnail_base,
+      tags: @record.snapshot_tag_names.join(' '),
+      parent: @record.parent,
+      original_created_from: @record.original_created_from,
+      original_created_before: @record.original_created_before }
   end
 end
diff --git a/backend/app/services/tag_version_recorder.rb b/backend/app/services/tag_version_recorder.rb
index b979462..fe2b0c1 100644
--- a/backend/app/services/tag_version_recorder.rb
+++ b/backend/app/services/tag_version_recorder.rb
@@ -14,9 +14,9 @@ class TagVersionRecorder < VersionRecorder
   def record_key = :tag
 
   def snapshot_attributes
-    { name: @tag.name,
-      category: @tag.category,
-      aliases: @tag.snapshot_aliases.join(' '),
-      parent_tag_ids: @tag.snapshot_parent_tag_ids.join(' ') }
+    { name: @record.name,
+      category: @record.category,
+      aliases: @record.snapshot_aliases.join(' '),
+      parent_tag_ids: @record.snapshot_parent_tag_ids.join(' ') }
   end
 end
diff --git a/backend/app/services/tag_versioning.rb b/backend/app/services/tag_versioning.rb
new file mode 100644
index 0000000..713cfeb
--- /dev/null
+++ b/backend/app/services/tag_versioning.rb
@@ -0,0 +1,26 @@
+class TagVersioning
+  def self.record! tag, event_type:, created_by_user:
+    if tag.nico?
+      NicoTagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+    else
+      TagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+    end
+  end
+
+  def self.record_tag_snapshot! tag, created_by_user:
+    event_type =
+        if tag.nico?
+          tag.nico_tag_versions.exists? ? :update : :create
+        else
+          tag.tag_versions.exists? ? :update : :create
+        end
+
+    record!(tag, event_type:, created_by_user:)
+  end
+
+  def self.record_tag_snapshots! tags, created_by_user:
+    tags.each do |tag|
+      record_tag_snapshot!(tag, created_by_user:)
+    end
+  end
+end
diff --git a/backend/app/services/version_recorder.rb b/backend/app/services/version_recorder.rb
index 5368313..3e1dc5c 100644
--- a/backend/app/services/version_recorder.rb
+++ b/backend/app/services/version_recorder.rb
@@ -9,7 +9,7 @@ class VersionRecorder
     validate_event_type!
   end
 
-  def record! record, event_type:, created_by_user:
+  def record!
     @record.with_lock do
       latest = latest_version