Our First Night: "Surprise in the bathroom"

Miki and Yuu's parents go for a trip, leaving Miki alone with Yuu. Yuu is talking a bath, while Miki is in her room waiting for the bath and writing to Meiko. Yuu comes in her room telling her that he's done giving her her turn. She takes a nice hot bath and apparently takes too long. She wraps the towel around herself and then faints. Yuu notices and runs down stairs. What does he do?