High school student Ryuji's older cousin Eriko returns from abroad to drag him to the scene of an underground transaction where he gets caught up in a shootout and car chase. While they thought they had stolen a miraculous Lost Precious from the criminal brokers, they ended up with a mysterious young girl. The young girl happily latches on to Ryuji even though they have never met. Who is this little girl? Thus begins the romance story of the beautiful young Rose and Ryuji.