Kenichi is often bullied at school, which causes him to always feel depressed and miserable at the start of each day. During this time, Kenichi's aunt, Mary, leaves her home and comes to stay at his house. It turns out that Mary, feeling neglected by her husband who has been too focused on work and not giving her any sexual attention, had an argument with him and left. Previously, Kenichi and Mary were very close, often taking baths together. While getting ready to take a bath, Mary suddenly hears Kenichi crying. Wanting to comfort him, she decides to join him in the bath, just like they used to. However, Kenichi is now a tall young man, and of course, his penis is very large, even bigger than her husband's! Mary had argued with her husband due to lack of sexual intimacy, so when she sees Kenichi's penis, her sexual desire is aroused, crossing the final boundary...