The protagonist of the tale is a boy named Haruka Nanase who adored swimming and diving into the ocean. He competed in a swimming competition with his swim club teammates Makoto Tachibana, Nagisa Hazuki, and Rin Matsuoka just before he finished elementary school. They split up after winning the competition.
After a while, during their uninteresting high school years, Rin resurfaces and challenges Haruka to a competition while showcasing his impressive strength. Haruka won't take this lying down and joins a swim club with Makoto, Nagisa and new member Rei Ryugazaki to battle Rin.
