Congratulations on becoming a working adult! A sister and brother, who are moving to Tokyo for work, try taking a family bath together for the first time in 10 years, with only a towel between them! They shouldn't be conscious of each other as members of the opposite sex, but they end up bathing together in a tiny bathtub! The extreme mission makes them aware of each other... and the close brother and sister end up having unprotected sex!