Amanchu!

The Story of Doing Something Bad With Hikari (1x2)

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On her way to school, Hikari races against her homeroom teacher, Mato Katori, who she discovers to be a fellow scuba diver. Later that day, Hikari drags Futaba to the school's Diving Club, where they try on some drysuits and take a dip in the pool. Moved by Hikari's high spirits, Futaba decides to join her in diving.