diff --git a/backend/app/controllers/nico_tags_controller.rb b/backend/app/controllers/nico_tags_controller.rb
index ca9a5b1..c897fe0 100644
--- a/backend/app/controllers/nico_tags_controller.rb
+++ b/backend/app/controllers/nico_tags_controller.rb
@@ -24,7 +24,12 @@ class NicoTagsController < ApplicationController
         ExternalTag
         .joins("LEFT JOIN (#{ post_tag_max_sql }) post_tag_max " \
                'ON post_tag_max.external_tag_id = external_tags.id')
-    q = q.where('external_tags.name LIKE ?', "%#{ name }%") if name
+    if name
+      q = q.where(('external_tags.name LIKE ? ' +
+                   "OR CONCAT(external_tags.platform, ':', external_tags.name) LIKE ?"),
+                  "%#{ name }%", "%#{ name }")
+    end
+
     if linked_tag
       linked_tag_ids =
           Tag
@@ -108,7 +113,10 @@ class NicoTagsController < ApplicationController
       updated_at: tag.created_at,
       deprecated_at: nil,
       aliases: [],
-      parents: [] }
+      parents: [],
+      has_wiki: false,
+      material_id: nil,
+      has_deerjikists: false }
   end
 
   def render_nico_tag_form_record_invalid record
diff --git a/backend/app/controllers/post_versions_controller.rb b/backend/app/controllers/post_versions_controller.rb
index 5d8d657..811227b 100644
--- a/backend/app/controllers/post_versions_controller.rb
+++ b/backend/app/controllers/post_versions_controller.rb
@@ -2,6 +2,9 @@ class PostVersionsController < ApplicationController
   def index
     post_id = params[:post].presence
     tag_id = params[:tag].presence&.to_i
+    external_tag_id = params[:external_tag].presence&.to_i
+    return head :bad_request if tag_id && external_tag_id
+
     page = (params[:page].presence || 1).to_i
     limit = (params[:limit].presence || 20).to_i
 
@@ -26,7 +29,12 @@ class PostVersionsController < ApplicationController
                 'prev.original_created_from AS prev_original_created_from',
                 'prev.original_created_before AS prev_original_created_before')
     q = q.where('post_versions.post_id = ?', post_id) if post_id
-    if tag_id
+    if external_tag_id || (tag_id && !(Tag.exists?(id: tag_id)))
+      q = q.where('JSON_CONTAINS(post_versions.tags_json,' +
+                  "JSON_OBJECT('external_tag_id', #{ external_tag_id })) " +
+                  'OR JSON_CONTAINS(prev.tags_json,' +
+                  "JSON_OBJECT('external_tag_id', #{ external_tag_id }))")
+    elsif tag_id
       q = q.where("JSON_CONTAINS(post_versions.tags_json, JSON_OBJECT('tag_id', #{ tag_id })) " +
                   "OR JSON_CONTAINS(prev.tags_json, JSON_OBJECT('tag_id', #{ tag_id }))")
     end
diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index daa68b2..e2e109d 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -505,7 +505,10 @@ class PostsController < ApplicationController
       memo[tag_id] = TagRepr.inline(tag).merge(children:, sections:)
     end
 
-    root_ids.filter_map { |id| build_node.call(id, []) }
+    internal_tags = root_ids.filter_map { |id| build_node.call(id, []) }
+    external_tags =
+        post.external_tags.map { ExternalTagRepr.inline(_1).merge(children: [], sections: []) }
+    internal_tags + external_tags
   end
 
   def sibling_posts_by_parent parent_post_ids
diff --git a/backend/app/representations/external_tag_repr.rb b/backend/app/representations/external_tag_repr.rb
new file mode 100644
index 0000000..d7e94f8
--- /dev/null
+++ b/backend/app/representations/external_tag_repr.rb
@@ -0,0 +1,20 @@
+module ExternalTagRepr
+  module_function
+
+  def base tag
+    { 'id' => tag.id,
+      'name' => "#{ tag.platform }:#{ tag.name }",
+      'category' => 'nico',
+      'post_count' => tag.post_count,
+      'created_at' => tag.created_at,
+      'updated_at' => tag.created_at,
+      'deprecated_at' => nil,
+      'aliases' => [],
+      'parents' => [],
+      'has_wiki' => false,
+      'material_id' => nil,
+      'has_deerjikists' => false }
+  end
+
+  def inline(tag) = base(tag)
+end
diff --git a/backend/app/representations/post_repr.rb b/backend/app/representations/post_repr.rb
index 79a1b1d..01206e4 100644
--- a/backend/app/representations/post_repr.rb
+++ b/backend/app/representations/post_repr.rb
@@ -87,15 +87,24 @@ module PostRepr
   end
 
   def tag_json post
-    post
+    internal_tags =
+        post
         .post_tags
         .reject { _1.tag.deprecated? }
         .sort_by { _1.tag.name }
-        .map do |post_tag|
-      TagRepr.inline(post_tag.tag).merge(
-          'children' => [],
-          'sections' => post_tag.sections.as_json(only: [:begin_ms, :end_ms]))
-    end
+        .map { |post_tag|
+          TagRepr.inline(post_tag.tag).merge(
+              'children' => [],
+              'sections' => post_tag.sections.as_json(only: [:begin_ms, :end_ms]))
+        }
+
+    external_tags =
+        post
+        .external_tags
+        .sort_by { _1.name }
+        .map { ExternalTagRepr.base(_1).merge('children' => [], 'sections' => []) }
+
+    internal_tags + external_tags
   end
 
   def thumbnail_url post, host: nil