A high school student named Makoto Saigi carries a deep distrust of anyone called sensei. When he was in kindergarten, he gave his favorite teacher a flower ring and a proposal, only for her to leave a few days later to get married. That betrayal shaped his entire outlook. At his new school, the prestigious Seikadai Academy, he is known for his hostile attitude toward teachers and is regularly sent to the guidance office. One day, the most popular teacher on campus, Maka Fujiki, calls him in. She is beautiful, elegant, and admired by the entire student body. Instead of scolding him, she confesses her love without warning. Makoto assumes it is a joke, but Maka is deadly serious. She declares that she will do everything in her power to make him fall for her, and if he ever says he loves her, she will quit teaching and become a nun.

Thus begins a forbidden love comedy in which Maka relentlessly pursues Makoto under the pretext of guidance counseling. She invites him to watch adult videos together, initiates excessive physical contact, and drags him on dates. Makoto struggles to resist, partly because he does not want to be responsible for ruining her career, but also because a small part of him starts to see past her perfect teacher facade. Maka lives next door and often visits his home, making escape impossible. She is a master of calculated sensual attacks, yet she also reveals a clumsy, earnest side that complicates Makoto's feelings.

Soon Makoto discovers he is not the only one who has caught feelings. A secret group of girls who call themselves SID (the Dead or Alive Alliance) also confess their love for him. The members include student council president Karen Jinsho, a serious honor student training to become a nun; classmate Nui Amanashi, a gravure idol who uses her charms without restraint; elementary school girl Muku Shinju, whose pure affection reminds Makoto of his own childhood; and his own younger sister Miharu Saiki, who pushes the boundaries of sibling affection. The SID girls have known about each other for some time and now coordinate their efforts to win Makoto, often competing directly with Maka.

The story unfolds through school events, holidays, and personal crises. Each major arc focuses on a different girl, exploring her backstory and the reason for her attachment to Makoto. The cultural festival features a lost school tradition named Firestorm that Makoto and another classmate revive. The Christmas season brings a triple date challenge between Makoto and the SID members, arranged with Maka's reluctant permission. A tennis exhibition match pits Maka against a current star player, with Makoto's sister caught in the middle. Throughout these events, Makoto's trauma is gradually addressed. He reencounters the woman from his kindergarten, now the mother of Muku, and learns the truth behind that old rejection. That reconciliation becomes a major emotional turning point.

The central conflict remains the graduation exam Maka herself posed. Every time Makoto feels his heart waver, he pulls back, afraid that his confession would end her teaching career. Maka, for her part, becomes increasingly torn between her sense of duty and her genuine love. She falls ill from overwork, and when Makoto saves her or rushes to her side, their bond deepens. Later, a near-fatal accident forces the truth into the open. By the end of the serialized arcs, Makoto finally confronts his feelings, and the relationship moves from a fake engagement to a real one. The manga continues past the original light novel's conclusion, exploring what happens after they become an official couple, with new challenges like Miharu's student council election and more elaborate group outings. The tone balances ecchi comedy with sincere romantic drama, and the cast of pursuers ensures the harem energy never fades.