Natsuki accompanies Atri who is on her way to school. However, when they arrive, they find that most of the school is underwater. Although they managed to get into the school building, inside it was full of empty classrooms and an unexpected teacher. There, Natsuki is faced with the saddening reality of the lives of the people who remained in their town.

Natsuki sets his heart on creating a tidal power generator that utilizes the ebb and flow of the ocean's tides. He dives back into the ocean to find some materials and salvages some resin from the ruins of Ryuuji's family's factory. As soon as he gets back he gets to work. As they are working, Natsuki and Ryuuji exchange heated opinions over how the generator should be built. Atri intervenes and the two guys become closer friends. Meanwhile, a suspicious-looking character peeks at them from outside of the school....

If Natsuki sells Atri, he can get batteries. However, he can no longer think of Atri as just an average humanoid. While he's deep in thought on the dock, looking out at the ocean, Natsuki finds Catherine floating in the water. She is completely intoxicated, and Natsuki and Atri take her in. But right at that time, the sound of a gunshot echoes within the silent ship.