The Story of the Girl and the Ocean (少女と海のコト Shōjo to Umi no Koto) is the debut episode of the Amanchu! anime.
We are introduced to a green-haired girl and her grandmother, both in the Amanchu Diving school. The younger one is looking out to the sea. The grandmother tells the girl that she'd give her pork soup after her dive. The green-haired girl cheerily agrees and sets out to dive with her 'secret weapon'. The grandmother muses to herself, saying that Hikari (the green-haired girl) would be starting high school soon.
A female raven-haired motorcyclist is seen driving close to the Amanchu shop, parks, walks down a few steps and ends up on a rock, overlooking the sea. She's on her phone the whole time, looking at pictures she took of her elementary school friends. The grandmother takes notice of her, and calls out to her. She tells the younger girl that she hasn't seen her before, and asks her if she's new around Ito. The raven-haired girl replies that she just moved here, and will be going to Yumegaoka Highschool (which is the same one Hikari will be going to).
Suddenly, air bubbles rise around the sea area of the rock she's sitting on. Basically, Hikari is down there, and the air bubbles are created by her 'secret weapon'. The girl on the rock doesn't know this, and tosses a rock down to where the bubbles originated; nearly hitting Hikari.