When Shūsuke gets a report about him failing in all of his subjects, he then realizes that he has to take a follow-up exam or risk having to take summer classes. Believing that she was the cause of Shūsuke's grade for calling him out each night, Mayuka feels guilty and offers to help him study for an upcoming exam. But while they were studying, Nao and Iroha decide to intrude on them. As Mayuka tries to get Shūsuke to study, Nao and Iroha compete to try and catch his attention. After some time later, Iroha presents surprise tickets for everyone to go to a local pool park if he passed, which encourages Shūsuke enough to pass. At the pool, Shūsuke spends most of his time teaching Mayuka how to swim, leaving Nao and Iroha pretty jealous. During that time, Mayuka becomes amorously focused with Shusuke's nipples, having never seen a man naked before.
Nao Takanashi loves her brother ShÅ«suke despite the incest taboo. Nao thinks that ShÅ«suke is her blood relative, but in fact she is an adopted daughter, whose parents have died. After Nao learns the fact, she wants to fall in love normally with ShÅ«suke because siblings by adoption can marry under the family law in Japan. However, she finds herself competing with ShÅ«suke's childhood friend, Iroha Tsuchiura, and his class president and yaoi lover, Mayuka KondÅ.
