During summer vacation, Shota and his family come to visit their relative Miyu's villa with a pool. Shota has to practice swimming for a school assignment, so Miyu teaches Miyu how to swim. However, when Miyu changes into her swimsuit, his penis becomes swollen due to her superb huge tits, and he loses his balance and can't swim. Miyu, who has no idea about this, tries her best to teach him how to swim, but...