When her dad gets a job overseas, Konatsu Amano has to leave the Tokyo life she's always known and relocate to a small seaside town to stay with her aunt. The move also means starting a new school surrounded by complete strangers, and it's a lot to handle for a girl who has trouble with change. But on her first day in her new town, Konatsu is instantly drawn to Koyuki, an older girl who is the sole member of the Aquarium Club. Konatsu's introverted tendencies are hard for her to overcome, but maybe she's found something worth coming out of her shell for?
Koyuki and Konatsu have both started to see the other as important, but they're still unable to be honest about their feelings. This leads to frustrating days when they're never in sync, and they begin to drift apart. Then one day Konatsu sees Koyuki and her classmate Kaede spending time together as if they're the best of friends, and she can't contain her agitation. Konatsu and Koyuki feel so strongly about each other that they feel uneasy even when there's nothing to worry about.