Itsuki Tagami is a teacher and colleague of Haruhiko Shimotsuki who instructs sports and coaches the swimming team. She works closely with the team's top performer, Chitose Misawa.

Tagami initially feels sympathy for Shimotsuki, though her feelings for him steadily intensify. After accidentally witnessing Shimotsuki and Chitose together sexually in the swimming pool shower, she suffers considerable emotional distress due to her own growing affection for him.

The incident leaves her conflicted in her interactions with Shimotsuki. Despite her turmoil, passion leads her to enter a physical relationship with him, though the conditions he imposes cause her profound shame.

Over time, Tagami gradually develops a similar dependency on Haruhiko, reflecting the dynamic he shares with Chitose. In a later encounter, she engages in a sexual act with both Chitose and Haruhiko. She has a beauty mark.