Koh Hikohiko, who had been living with his aunt Ai, announces his desire to live alone after landing a job. Hearing this, Ai, desperate to keep him close, confides in Yamane, her coworker. One day, Hikohiko notices moans coming from Ai's bedroom and peeks inside—only to discover Ai secretly meeting with Yamane. Witnessing the scene shakes Hikohiko deeply. Unable to contain his arousal back in his room, he begins stroking his hard cock when suddenly Ai appears. She deliberately enters, then starts teasing his erect penis. This moment sparks a dramatic shift in their relationship.