The protagonist awakens with amnesia, disoriented in an unfamiliar room, hearing a girl's voice. He discovers he's in a different, strikingly handsome body and is called "Yusei" by a girl named Yui, who claims to be his younger sister. Overwhelmed by confusion and a complete lack of personal memory, he notices subtle differences in his home.
He finds a mysterious, ornate diary on his desk, feeling an inexplicable compulsion to read it. The diary, written by "someone" about his "previous self," details his past as an ordinary high school student with a passion for food touring. His life-changing event was discovering a "Pudding of Bliss." The diary recounts his "death" shielding this pudding from a car, and a voice explaining he was transferred to a "similar but different adjacent world" by a "Diary of Wishes" to grant his desire for undisturbed delicious food. Yusei finds this account absurd, yet the strange reality of his new body and the world around him makes him question everything.
The diary proves to be a magical system, responding to his thoughts. When he wishes for a "resume," a profile for "Takeda Yusei" appears, detailing his age (16), height, and family: a father overseas, a mother overseas (due to a promotion), and his sister Yui, with whom he now lives. His parents are in a "visiting marriage," a common practice in this world. The diary also reveals "Holder Skills" like maintaining composure and a "Blessing of the Pudding God." Yusei discovers this world is a version of Japan that diverged after the Heisei era due to a giant meteorite, leading to a drastic decline in male birth rates (a 1:8 male-to-female ratio). Society is female-dominated, with male rights now protected after a past "old man abandonment" era.
Yusei learns he's a transfer student to Eika Shuei Academy, a "Male Preferential Treatment School" where his presence was eagerly anticipated due to the scarcity of male students. The school offers significant advantages to males, including guaranteed university admission, while female students fiercely compete academically for placement in mixed-gender classes. He also discovers the school is a "marriage hunting" ground, as men can have multiple wives (up to 12), and many of his new male classmates are already married or engaged at 16. Yusei is shocked by this revelation and the intense social dynamics.
On his first day, Yusei is overwhelmed by the attention from female students, who perceive him as a "prince." He also discovers a new "skill": transparent profiles of people he talks to appear in his vision, detailing their marital status and "empty marriage slots," further solidifying the game-like nature of his new reality. He finds his shoe locker overflowing with love letters. Despite the strangeness, Yusei, guided by his responsible sister Yui, begins to navigate his new life, trying to understand the rules of this bizarre world and his place within it, while grappling with his lost memories and newfound identity as a highly sought-after male.
