Itsuki is a serious university student who wants to become a teacher. When she collapses from anemia, she is rescued by Kazuma, a handsome and seemingly kind fellow student who is the same age. The two begin dating, and Itsuki quickly falls for him, describing him as a perfect prince who saved her from a crisis. Her friends worry she is being played, but Itsuki grows more infatuated. Kazuma, however, has a hidden side shaped by a painful past.

Kazuma was raised by his father, a host named Togo, who died of illness when Kazuma was four years old. After Togo's death, one of his clients, a married woman, took Kazuma into her home, where she lived with her husband and son, Yuto. Kazuma became Yuto's younger stepbrother. While young Kazuma was clingy and attached to Yuto, and Yuto initially cared for his non-blood brother, Yuto eventually insulted and looked down on Kazuma's deceased father. This planted a seed of revenge. Yuto later grew up in a dysfunctional family environment that gradually corroded his heart until he met Itsuki at a university drinking party, which brought change to his boring daily life. Kazuma's ultimate plan is to take revenge against Yuto by stealing the first girl Yuto ever loved: Itsuki.

The story follows Itsuki after she graduates and becomes a teacher, still unable to stop thinking about Kazuma even as she tries to be a good educator. Kazuma continues to insert himself into her life, including a tense scene in the school infirmary where he pulls her into a hug just as someone else enters. The narrative alternates to reveal the backstory of Kazuma and Yuto's intertwined family history, the trauma of being raised in a broken home with a deceased host father, and the calculated revenge that drives Kazuma to pursue Itsuki not out of love but as a weapon against his brother. The series is a romantic labyrinth in which Itsuki is toyed with by handsome men whose true motives are hidden behind charming exteriors.