Noticing Futaba struggling with strength, Mato has her and Hikari go jogging to build up strength. Along the way, they come across some students from diving school, Ai and Makoto Ninomiya, who turn out to be their upperclassmen in the Diving Club. After a hectic first meeting, Ai holds a meeting to discuss how Futaba will be aiming for an Open Water Diver Certification, which somehow ends in a chalk drawing session.

Makoto becomes concerned when Ai receives what appears to be a love letter from her classmate, only to later find it was addressed to another girl. Later, as Futaba and Hikari take part in various fitness exams, Hikari helps Futaba improve her self-confidence during the 1000m run.

The Open Diver course begins, with Futaba and Hikari paired up as buddies. Futaba loses one of her fins on the way to the descent point, but it gets picked up by another diver, turning her fears of the unknown world beneath her into excitement. Guided by the bubbles of the other divers, Futaba reaches the bottom of the ocean floor, wowed by the scenery and sealife spread out before her. Clearing all the tasks before her, Futaba passes the course with flying colors and becomes a fully-fledged Open Diver. Afterwards, Futaba and Hikari thank each other for everything that's happened since they became friends.