After her family's business collapses, high school student Shu Kosaka is forced to transfer schools under a scholarship that covers tuition and dorm fees. The catch is that the school, Nijisei Gakuen, was an all-boys school until very recently, making Shu the only female student on campus. Having been bullied by boys in her past, Shu harbors a deep fear of male students, yet she has no choice but to endure the situation. The school's dormitory, still a boys' dorm, places her in constant vulnerability. Among the male students, the most conspicuous and cool-headed is Rensei Shiba. He first appears cold and mean, treating Shu with indifference. However, when Shu reaches her breaking point from the harassment and isolation, Shiba steps in and declares, "I'll protect you." Beneath his gruff exterior, Shiba is unexpectedly kind, and his protective nature stirs Shu's memories of her first love from childhood. Unbeknownst to Shu, Shiba is that same boy who shielded her from bullies years ago, though he remembers her clearly. As they navigate life together in the boys' dorm, Shu gradually learns to trust him, and the two grow closer, rekindling the feelings they once had. Their relationship faces multiple challenges, including a jealous classmate named Akito Kamo, who was involved in Shu's past bullying and now seeks to claim her. Akito's rivalry with Shiba culminates in a physical confrontation during the sports festival, after which Akito reluctantly steps back. Later, Shu starts a part-time job at a café where Shiba works and meets a female coworker named Sakura, who falsely claims to have been Shiba's first experience, creating misunderstandings between the couple. Shu's insecurity and Sakura's manipulation lead to a tense period where Shu pushes Shiba away. Eventually, Shiba clarifies the truth, and they reconcile. Meanwhile, Shiba's father, a strict politician, pressures him to return home and abandon his life at school. When Shiba's father falls gravely ill, Shiba is forced to leave school to care for him and is told to distance himself from Shu. Heartbroken but determined, Shu waits for him. Shiba's friend Isshin develops feelings for Shu during this time and briefly confesses, but Shu's heart remains with Shiba. After Shiba's father passes away, Shu rushes to his side, and the two reunite, affirming their commitment to each other. The story concludes with Shu and Shiba overcoming the barriers of family expectations, past trauma, and external rivals, choosing to continue their love story together.