After her father traveled overseas for work, Konatsu Amano moved to Iyo-Nagahama to live with her aunt. On the way to her aunt's house, she gets dragged into her new high school's aquarium open house. It is there where she meets Koyuki Honami, a pretty upperclassman. After encountering each other a few more times, the girls quickly become infatuated with one another. In an attempt to get closer to Koyuki, Konatsu joins the aquarium club, which previously had Koyuki as the only member.

Konatsu and Koyuki are similar in many ways. They both feel an acute sense of loneliness, are kind and thoughtful, and yet are also reserved and stubborn. The latter qualities make the girls hesitant to share their feelings, leading to complications in their friendship. To move forward, the girls will have to figure out what they mean to each other and how to navigate their emotions. Will loneliness remain their sole companion, or will Konatsu and Koyuki find the courage to face themselves and each other?