The two sisters, Ayane and Kotone, decide to move in with their “brother” and former childhood friend Kazushi without asking his opinion. Kazushi is not really related to the two but sees them as part of the family. After the part-time student uses one of Ayane and Kotone’s bath salts, they get angry and unceremoniously get into the water with him to get something out of the experience as well. In the process, the three of them become unintentionally closer than they thought, despite their barely-there swimming costumes …