diff --git a/internal/translator/kiro/claude/kiro_claude_request.go b/internal/translator/kiro/claude/kiro_claude_request.go
index c3c359e0..7012e644 100644
--- a/internal/translator/kiro/claude/kiro_claude_request.go
+++ b/internal/translator/kiro/claude/kiro_claude_request.go
@@ -586,6 +586,17 @@ func processMessages(messages gjson.Result, modelID, origin string) ([]KiroHisto
 
 	// Merge adjacent messages with the same role
 	messagesArray := kirocommon.MergeAdjacentMessages(messages.Array())
+
+	// FIX: Kiro API requires history to start with a user message.
+	// Some clients (e.g., OpenClaw) send conversations starting with an assistant message,
+	// which is valid for the Claude API but causes "Improperly formed request" on Kiro.
+	// Prepend a placeholder user message so the history alternation is correct.
+	if len(messagesArray) > 0 && messagesArray[0].Get("role").String() == "assistant" {
+		placeholder := `{"role":"user","content":"."}`
+		messagesArray = append([]gjson.Result{gjson.Parse(placeholder)}, messagesArray...)
+		log.Infof("kiro: messages started with assistant role, prepended placeholder user message for Kiro API compatibility")
+	}
+
 	for i, msg := range messagesArray {
 		role := msg.Get("role").String()
 		isLastMessage := i == len(messagesArray)-1