Itsuki Tagami serves as a physical education teacher and swimming team advisor at Haruhiko Shimotsuki's school. She coaches the team's top performer, Chitose Misawa, fostering a close working relationship between them. Tagami initially feels sympathy for Shimotsuki, but these feelings gradually intensify into romantic affection.

Discovering an intimate encounter between Shimotsuki and Chitose in the school showers causes Tagami significant emotional distress, given her deepened feelings for him. This event creates internal conflict affecting her interactions with Shimotsuki. Despite this turmoil, she eventually enters into a physical relationship with him under conditions that evoke deep shame.

Tagami becomes caught in a dynamic mirroring Chitose's dependency on Shimotsuki, characterized by compromised agency. Later, she participates in a three-way encounter involving Shimotsuki and Chitose.

Physically, Tagami has brown shoulder-length hair and blue or violet eyes, standing 161 cm tall with measurements of 91-60-87 cm. A mole is present on her body. Her typical attire includes professional clothing like a blazer and miniskirt, complemented by a coaching whistle and a sports swimsuit.