During summer vacation, Shota was invited by his friends to go swimming in the sea, but the beach was closed, so the plan was canceled. Feeling sorry for Shota and his friends, who were extremely disappointed, Riho, the sister of one of his friends, decided to buy a home pool... As Shota watched Riho's swimsuit, which barely covered her overflowing buttocks, his little Shota began to swell up vigorously!