Kazuki Sonomiya, sometimes identified as Itsuki Sonomiya, is a Japanese high school student distinguished by brown hair and brown eyes and possessing an average physical build. He primarily wears his school uniform for academic pursuits and various casual attire outside of school hours. His existence is defined by a global pandemic that triggered widespread male impotency through a virus and later vaccine side effects. Kazuki is one of the exceptionally rare males naturally immune to this condition, rendering him biologically unique in this altered world. This immunity necessitates his transfer to a specialized high school with a predominantly female student body, where he serves as the sole functional male among four billion affected females. Key relationships drive his narrative. He loses his virginity to Akari Himeno, a kind and supportive upperclassman conflicted by her attraction to him. He subsequently engages in sexual relationships with multiple other women: Kaede Shiina, his teacher; Aki Kokonoe, a tomboyish athlete classmate; and Yui Kurumizawa, a wealthy heiress classmate. These interactions arise directly from his unique biological status and the societal pressures following the pandemic. Personality-wise, Kazuki embodies a typical horny teenager. Initially overwhelmed by the intense female attention, he gradually learns to navigate the complex social and romantic entanglements resulting from his situation. His documented character development remains limited to these immediate reactions within the harem dynamics.