Hikari Kohinata is a cheerful 15 year-old girl
who lives near the ocean and she spends much of her time diving as a result.
On her first day of high school,
she meets a teacher who also likes scuba diving.
There’s also a 16 year-old classmate, Futaba Ooki,
who gets dragged along in Hikari’s maelstrom as soon as they meet at school.