Natsuo's life suddenly becomes more complicated when his father comes home and announces he has remarried a woman with two daughters whom Natsuo has met before. They're Hina, his teacher and unrequited crush, and Rui, a girl he previously slept with.
Natsuo learned the truth about Hina's mysterious relationship. Following an intense encounter with her, Natsuo leaves home to cool off and establishes a connection with Rui.
Natsuo's perception of Hina changes when she reveals how she first met Shuu. Later, Rui comes to Natsuo with a surprising request - one he isn't sure he should fulfill.
Hina puts her plan to move out into motion. Neither Rui nor Natsuo wants her to leave, albeit for different reasons. Will their home feel the same without Hina in it?
Rui makes a decision after her conversation with Natsuo. Later, Natsuo's class takes a field trip to Okinawa, where feelings are laid bare beneath the light of fireworks.
