Thief's kiss becomes available only after the Worldly Desire Temple events. After the Wooden Gong Incident, return and speak with Bell and she'll send back to Julie's bar. Look in Thief's hole afterward. In the morning, talk to Policeman and then talk to Julie when she's awake. Wait for Thief to enter and exit Julie's. He'll get stuck trying to re-enter the alley. Speak to him and he'll attack you with his bag. Then he'll toss it away and run into the alley. Follow after him and he'll be in Viva.