Shōta Doi, originally nicknamed "Dojii," was a third-year student at Keimon West Private High School prior to entering cryostasis. Suffering from the life-threatening degenerative disease cellular sclerosis, he endured relentless physical bullying from classmates Takamatsu and Erika, including abuse like cigar burns. Introverted and isolated, Shōta lacked friends and formed a deep emotional dependence on his teacher, Yuzuki Hanyu. His family consisted of a divorced mother, a work-preoccupied father, and a younger sister, Mayu, living in America.

Awakening in 2045, Shōta discovered the MK Virus had killed 99.9% of males. Immune, he became one of five surviving men tasked with repopulation. Assigned secretary Karen Kamiya facilitated his transition into a girls' high school, where he initially struggled with social anxiety. His attachment to Yuzuki intensified, leading him to select her as his first partner, resulting in her pregnancy. Shōta gradually grew more assertive, leveraging his status to pursue relationships with classmates Shunka Hiiragi (bonding over shared bullying), Natsu Ichijō, and Akira Tōdō.

Shōta's trauma fueled vengeful acts against former tormentors. He had Erika transferred to his school, keeping her chained as a "pet" and subjecting her to humiliation and abuse, including forced observation of his mating sessions. Similarly, he publicly mated with Shion Hoshino on a rooftop to mirror her past indifference to his suffering, embracing sadistic gratification and his newfound power.

Following a terrorist bomb attack, Shōta underwent physical reconstruction in a growth device, emerging taller and free of his glasses. This "Neo-Shota" phase coincided with rising political ambition. Manipulated by Karen Kamiya, he supported ethically contentious initiatives like accelerated growth experiments on male infants. By the series' conclusion, Shōta ascended to president of the Japanese republic, consolidating authority while facing opposition from figures like Reito Mizuhara over his methods.