diff --git a/app/javascript/controllers/form_controller.js b/app/javascript/controllers/form_controller.js
index f917bd092..beca1f08f 100644
--- a/app/javascript/controllers/form_controller.js
+++ b/app/javascript/controllers/form_controller.js
@@ -8,10 +8,21 @@ export default class extends Controller {
     debounceTimeout: { type: Number, default: 300 }
   }
 
+  #isComposing = false
+
   initialize() {
     this.debouncedSubmit = debounce(this.debouncedSubmit.bind(this), this.debounceTimeoutValue)
   }
 
+  // IME Composition tracking
+  compositionStart() {
+    this.#isComposing = true
+  }
+
+  compositionEnd() {
+    this.#isComposing = false
+  }
+
   submit() {
     this.element.requestSubmit()
   }
@@ -32,6 +43,12 @@ export default class extends Controller {
     }
   }
 
+  preventComposingSubmit(event) {
+    if (this.#isComposing) {
+      event.preventDefault()
+    }
+  }
+
   debouncedSubmit(event) {
     this.submit(event)
   }
diff --git a/app/javascript/controllers/navigable_list_controller.js b/app/javascript/controllers/navigable_list_controller.js
index 4af794c4b..bd5e87665 100644
--- a/app/javascript/controllers/navigable_list_controller.js
+++ b/app/javascript/controllers/navigable_list_controller.js
@@ -245,6 +245,9 @@ export default class extends Controller {
       }
     },
     Enter(event) {
+      // Skip handling during IME composition (e.g., Japanese input)
+      if (event.isComposing) { return }
+
       if (event.shiftKey) {
         this.#toggleCurrentItem(event)
       } else {
diff --git a/app/views/cards/comments/reactions/new.html.erb b/app/views/cards/comments/reactions/new.html.erb
index 38c6daf98..8cc5dda73 100644
--- a/app/views/cards/comments/reactions/new.html.erb
+++ b/app/views/cards/comments/reactions/new.html.erb
@@ -2,14 +2,14 @@
   <%= form_with model: [ @comment.card, @comment, Reaction.new ],
         class: "reaction reaction__form expanded",
         html: { aria: { label: "New reaction" } },
-        data: { controller: "form reaction-emoji", turbo_frame: dom_id(@comment, :reacting), action: "keydown.esc->form#cancel submit->form#preventEmptySubmit" } do |form| %>
+        data: { controller: "form reaction-emoji", turbo_frame: dom_id(@comment, :reacting), action: "keydown.esc->form#cancel submit->form#preventEmptySubmit submit->form#preventComposingSubmit" } do |form| %>
     <label class="reaction__form-label flex gap" style="--column-gap: 0.4ch;">
       <figure class="reaction__avatar margin-none flex-item-no-shrink">
         <%= avatar_tag Current.user %>
       </figure>
 
       <%= form.text_field :content, autofocus: true, autocomplete: "off", autocorrect: "off", maxlength: 16,
-            pattern: /\S+.*/, class: "input reaction__input txt-small", data: { form_target: "input", reaction_emoji_target: "input" }, aria: { label: "Add a reaction" } %>
+            pattern: /\S+.*/, class: "input reaction__input txt-small", data: { form_target: "input", reaction_emoji_target: "input", action: "compositionstart->form#compositionStart compositionend->form#compositionEnd" }, aria: { label: "Add a reaction" } %>
     </label>
 
     <%= render "cards/comments/reactions/menu", comment: @comment %>
diff --git a/app/views/cards/display/perma/_steps.html.erb b/app/views/cards/display/perma/_steps.html.erb
index 36ce68fc5..9f65dec2a 100644
--- a/app/views/cards/display/perma/_steps.html.erb
+++ b/app/views/cards/display/perma/_steps.html.erb
@@ -4,8 +4,8 @@
   <% unless card.closed? %>
     <li id="<%= dom_id(card, :new_step) %>" class="step">
       <input type="checkbox" class="step__checkbox" disabled>
-      <%= form_with model: [card, Step.new], url: card_steps_path(card), class: "min-width", data: { controller: "form", action: "submit->form#preventEmptySubmit turbo:submit-end->form#reset" } do |form| %>
-        <%= form.text_field :content, class: "input step__content hide-focus-ring", placeholder: "Add a step…", autocomplete: "off", data: { form_target: "input", "1p-ignore": "true" }, aria: { label: "Add a step" } %>
+      <%= form_with model: [card, Step.new], url: card_steps_path(card), class: "min-width", data: { controller: "form", action: "submit->form#preventEmptySubmit submit->form#preventComposingSubmit turbo:submit-end->form#reset" } do |form| %>
+        <%= form.text_field :content, class: "input step__content hide-focus-ring", placeholder: "Add a step…", autocomplete: "off", data: { form_target: "input", "1p-ignore": "true", action: "compositionstart->form#compositionStart compositionend->form#compositionEnd" }, aria: { label: "Add a step" } %>
       <% end %>
     </li>
   <% end %>
diff --git a/app/views/cards/taggings/new.html.erb b/app/views/cards/taggings/new.html.erb
index 644b29d2b..b8ff47df6 100644
--- a/app/views/cards/taggings/new.html.erb
+++ b/app/views/cards/taggings/new.html.erb
@@ -11,10 +11,10 @@
 
     <%= form_with url: card_taggings_path(@card),
           id: dom_id(@card, :tags_form),
-          data: { controller: "form", action: "submit->form#preventEmptySubmit" },
+          data: { controller: "form", action: "submit->form#preventEmptySubmit submit->form#preventComposingSubmit" },
           class: "flex flex-column gap-half full-width margin-block-half" do |form| %>
       <%= form.text_field :tag_title, placeholder: @tags.any? ? "Add a new tag or filter…" : "Name this tag…", class: "input txt-small full-width",
-            autocomplete: "off", autofocus: true, data: { filter_target: "input", form_target: "input", action: "input->filter#filter" } %>
+            autocomplete: "off", autofocus: true, data: { filter_target: "input", form_target: "input", action: "input->filter#filter compositionstart->form#compositionStart compositionend->form#compositionEnd" } %>
     <% end %>
 
     <ul class="popup__list" data-filter-target="list">