diff --git a/.ruby-version b/.ruby-version
index 3b47f2e..2aa5131 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-3.3.9
+3.4.7
diff --git a/Gemfile b/Gemfile
index f3bd56a..de247cf 100644
--- a/Gemfile
+++ b/Gemfile
@@ -2,6 +2,8 @@ source "https://rubygems.org"
 
 ruby file: '.ruby-version'
 
+gem 'nkf'
+
 # Bundle edge Rails instead: gem "rails", github: "rails/rails", branch: "main"
 gem "rails", "~> 8.0.0"
 
diff --git a/Gemfile.lock b/Gemfile.lock
index 69223ac..2832e3f 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -167,6 +167,7 @@ GEM
     net-smtp (0.5.1)
       net-protocol
     nio4r (2.7.4)
+    nkf (0.2.0)
     nokogiri (1.18.10-aarch64-linux-gnu)
       racc (~> 1.4)
     nokogiri (1.18.10-aarch64-linux-musl)
@@ -343,6 +344,7 @@ DEPENDENCIES
   capybara
   debug
   importmap-rails
+  nkf
   pg
   puma (>= 5.0)
   rails (~> 8.0.0)
@@ -356,7 +358,7 @@ DEPENDENCIES
   web-console
 
 RUBY VERSION
-   ruby 3.3.9p170
+   ruby 3.4.7p58
 
 BUNDLED WITH
-   2.5.22
+   2.7.2