Yu Aoba has a secret problem. He's sexually attracted to his own mother, Mieko. Her tendency to wear revealing clothes during summer only adds to his turmoil.

One day, Yu starts inviting his friend, Taiki Shimosaka, to hang out at his place. However, Yu can't relax with Taiki around because his welcoming mother continues to dress skimpily. Soon, they are joined by Hinano Izawa, a girl who is an acquaintance of Taiki.

One day, Yu's secret stash of adult videos featuring women who look like his mother is discovered by his two friends. Embarrassed and guilt-ridden after being called out for his "mother complex," Yu is mortified.

Despite this, their three-way friendship continues, and Yu eventually finds himself alone with Hinano. She teases him about his mother complex and declares, "I'll set you straight," implying that his feelings are purely sexual.

From that day forward, Yu and Hinano begin a physical relationship under the guise of study sessions. Yu finds himself addicted to their secret acts, fueled by a sense of forbidden pleasure. However...

Unbeknownst to him, his mother, Mieko and Taiki start spending an increasing amount of time together...