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....
But then why did Grandma have 
her hidden away so carefully?
لكن لماذا أخفتها جدّتي بحرص شديد؟
Pero ¿por qué la conservó
con tanto cuidado la abuela?
Pero ¿por qué la conservó
con tanto cuidado la abuela?
Mais pourquoi ma grand-mère
a-t-elle conservé Atri si précieusement ?
Però, comunque,
Mas então por que será que minha vó
escondeu ela com tanto cuidado?
Только вот… почему бабушка
так берегла её?