diff --git a/shared/godot/chat/chat_display.gd b/shared/godot/chat/chat_display.gd
index 7500789..1becdf0 100644
--- a/shared/godot/chat/chat_display.gd
+++ b/shared/godot/chat/chat_display.gd
@@ -1,6 +1,7 @@
 extends VBoxContainer
 ## Renders chat messages using a single RichTextLabel with BBCode.
 ## Handles its own scrolling and text selection — no ScrollContainer needed.
+## Supports mark_speaking() to underline the currently-playing TTS sentence.
 
 const SELECTION_BG_COLOR := Color("#1A5C56")
 
@@ -12,9 +13,21 @@ const EMOTION_HEX: Dictionary = {
 	"relaxed": "#80CBC4",
 }
 
+class _Msg:
+	var role: String        # "user" | "assistant" | "error"
+	var emotion: String     # assistant only
+	var parts: Array[String] # sentences (assistant) or [text] (user/error)
+
+	func _init(p_role: String, p_emotion: String = "") -> void:
+		role = p_role
+		emotion = p_emotion
+		parts = []
+
+
 var _rtl: RichTextLabel
-var _has_messages: bool = false
-var _current_emotion: String = "neutral"
+var _messages: Array[_Msg] = []
+var _speaking_msg: int = -1
+var _speaking_part: int = -1
 
 
 func setup() -> void:
@@ -45,13 +58,115 @@ func setup() -> void:
 	add_child(_rtl)
 
 
-func _separator() -> void:
-	if _has_messages:
-		_rtl.append_text("\n\n")
+var message_count: int:
+	get:
+		return _messages.size()
 
 
 func add_user_message(text: String) -> void:
-	_separator()
+	var msg := _Msg.new("user")
+	msg.parts.append(text)
+	_messages.append(msg)
+	_append_user_block(text)
+	_scroll_to_bottom()
+
+
+func start_miku_message(emotion: String) -> void:
+	var msg := _Msg.new("assistant", emotion)
+	_messages.append(msg)
+	_append_miku_header(emotion)
+
+
+func append_miku_text(text: String) -> void:
+	var msg: _Msg = _messages.back()
+	msg.parts.append(text)
+	_rtl.append_text("[color=%s]%s[/color]" % [UiTheme.text_primary.to_html(false), _escape(text)])
+	_scroll_to_bottom()
+
+
+func update_miku_emotion(emotion: String) -> void:
+	if _messages.is_empty():
+		return
+	var msg: _Msg = _messages.back()
+	if msg.role == "assistant":
+		msg.emotion = emotion
+
+
+func add_error_message(text: String) -> void:
+	var msg := _Msg.new("error")
+	msg.parts.append(text)
+	_messages.append(msg)
+	_append_error_block(text)
+	_scroll_to_bottom()
+
+
+func add_assistant_message(text: String, emotion: String = "neutral") -> void:
+	start_miku_message(emotion)
+	append_miku_text(text)
+
+
+func mark_speaking(msg_idx: int, part_idx: int) -> void:
+	_speaking_msg = msg_idx
+	_speaking_part = part_idx
+	_render()
+
+
+func clear_messages() -> void:
+	_rtl.clear()
+	_messages.clear()
+	_speaking_msg = -1
+	_speaking_part = -1
+
+
+func _render() -> void:
+	_rtl.clear()
+	for i: int in _messages.size():
+		var msg: _Msg = _messages[i]
+		if i > 0:
+			_rtl.append_text("\n\n")
+		match msg.role:
+			"user":
+				(
+					_rtl
+					. append_text(
+						(
+							"[right][color=%s]You[/color]\n[color=%s]%s[/color][/right]"
+							% [
+								UiTheme.text_muted.to_html(false),
+								UiTheme.text_primary.to_html(false),
+								_escape(msg.parts[0]),
+							]
+						)
+					)
+				)
+			"assistant":
+				var accent_hex: String = EMOTION_HEX.get(msg.emotion, UiTheme.accent.to_html(false))
+				_rtl.append_text(
+					(
+						"[color=%s]✦ Miku[/color] [color=%s]● %s[/color]\n"
+						% [UiTheme.accent.to_html(false), accent_hex, msg.emotion]
+					)
+				)
+				for j: int in msg.parts.size():
+					var part: String = msg.parts[j]
+					if i == _speaking_msg and j == _speaking_part:
+						_rtl.append_text(
+							"[u][color=%s]%s[/color][/u]" % [UiTheme.text_primary.to_html(false), _escape(part)]
+						)
+					else:
+						_rtl.append_text(
+							"[color=%s]%s[/color]" % [UiTheme.text_primary.to_html(false), _escape(part)]
+						)
+			"error":
+				_rtl.append_text(
+					"[color=#D45F5F]⚠[/color] [color=#FF9999]%s[/color]" % _escape(msg.parts[0])
+				)
+	_scroll_to_bottom()
+
+
+func _append_user_block(text: String) -> void:
+	if _rtl.get_parsed_text().length() > 0:
+		_rtl.append_text("\n\n")
 	(
 		_rtl
 		. append_text(
@@ -65,47 +180,24 @@ func add_user_message(text: String) -> void:
 			)
 		)
 	)
-	_has_messages = true
-	_scroll_to_bottom()
 
 
-func start_miku_message(emotion: String) -> void:
-	_current_emotion = emotion
+func _append_miku_header(emotion: String) -> void:
+	if _rtl.get_parsed_text().length() > 0:
+		_rtl.append_text("\n\n")
 	var accent_hex: String = EMOTION_HEX.get(emotion, UiTheme.accent.to_html(false))
-	_separator()
 	_rtl.append_text(
 		(
 			"[color=%s]✦ Miku[/color] [color=%s]● %s[/color]\n"
 			% [UiTheme.accent.to_html(false), accent_hex, emotion]
 		)
 	)
-	_has_messages = true
 
 
-func append_miku_text(text: String) -> void:
-	_rtl.append_text("[color=%s]%s[/color]" % [UiTheme.text_primary.to_html(false), _escape(text)])
-	_scroll_to_bottom()
-
-
-func update_miku_emotion(emotion: String) -> void:
-	_current_emotion = emotion
-
-
-func add_error_message(text: String) -> void:
-	_separator()
+func _append_error_block(text: String) -> void:
+	if _rtl.get_parsed_text().length() > 0:
+		_rtl.append_text("\n\n")
 	_rtl.append_text("[color=#D45F5F]⚠[/color] [color=#FF9999]%s[/color]" % _escape(text))
-	_has_messages = true
-	_scroll_to_bottom()
-
-
-func add_assistant_message(text: String, emotion: String = "neutral") -> void:
-	start_miku_message(emotion)
-	append_miku_text(text)
-
-
-func clear_messages() -> void:
-	_rtl.clear()
-	_has_messages = false
 
 
 func _scroll_to_bottom() -> void:
diff --git a/shared/godot/chat/chat_window.gd b/shared/godot/chat/chat_window.gd
index f1ce15c..77fcc82 100644
--- a/shared/godot/chat/chat_window.gd
+++ b/shared/godot/chat/chat_window.gd
@@ -29,6 +29,8 @@ var _status_label: Label
 var _conversation_list: VBoxContainer
 var _miku_streaming: bool = false
 var _replay_regex: RegEx
+var _current_miku_msg_idx: int = -1
+var _speaking_sentence_idx: int = -1
 
 
 func setup() -> void:
@@ -37,6 +39,7 @@ func setup() -> void:
 	EventBus.sentence_ready.connect(_on_sentence_ready)
 	EventBus.state_changed.connect(_on_state_changed)
 	EventBus.emotion_changed.connect(_on_emotion_changed)
+	EventBus.audio_started.connect(_on_audio_started)
 
 
 func _ready() -> void:
@@ -140,6 +143,8 @@ func replay_messages(messages: Array[Dictionary]) -> void:
 func clear_conversation() -> void:
 	_display.clear_messages()
 	_miku_streaming = false
+	_current_miku_msg_idx = -1
+	_speaking_sentence_idx = -1
 
 
 func show_error(message: String) -> void:
@@ -171,6 +176,8 @@ func _on_text_submitted_display(text: String) -> void:
 
 func _on_sentence_ready(text: String, emotion: String) -> void:
 	if not _miku_streaming:
+		_current_miku_msg_idx = _display.message_count
+		_speaking_sentence_idx = -1
 		_display.start_miku_message(emotion)
 		_miku_streaming = true
 	var trimmed := text.strip_edges()
@@ -178,11 +185,19 @@ func _on_sentence_ready(text: String, emotion: String) -> void:
 		_display.append_miku_text(trimmed + " ")
 
 
+func _on_audio_started() -> void:
+	_speaking_sentence_idx += 1
+	_display.mark_speaking(_current_miku_msg_idx, _speaking_sentence_idx)
+
+
 func _on_state_changed(_from: String, to: String) -> void:
 	if _status_label != null:
 		_status_label.text = STATE_LABELS.get(to, "")
 	if to == "idle":
 		_miku_streaming = false
+	if to in ["idle", "listening", "processing"]:
+		_speaking_sentence_idx = -1
+		_display.mark_speaking(-1, -1)
 
 
 func _on_emotion_changed(emotion: String) -> void: