The Story of the Blue World
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.
Aired 23/09/2016EP 12 - The Story of the Blue World

Amanchu!
Hikari Kohinata is an overwhelmingly cheerful and outgoing 15-year-old girl who has spent all her life in a small and beautiful seaside town on the Izu peninsula. On the first day of high school, she meets Futaba Oki, a slightly introverted girl who has just moved from Tokyo. Before she knows it, Futaba gets dragged along into Hikari's passion for scuba diving. And from there, Futaba gradually starts to come out of her shell, and learns how to take challenges and dive into the ocean of life.
(Source: Anime News Network)