Fumiya Kurimoto is Natsuo Fujii's childhood friend and closest confidant, their bond stretching back to kindergarten when their families lived in the same apartment complex. They shared classes before high school and maintained their connection despite later attending different schools. He lives with his mother and a younger sister, both sharing his strong physical resemblance. His father is not mentioned.

Stockier than Natsuo, Fumiya almost always wears glasses and keeps a neatly trimmed professional haircut. Despite his appearance, he overpowers Natsuo during their occasional wrestling matches. His personality centers on deep loyalty and concern for Natsuo's well-being. He consistently offers support: providing refuge during Natsuo's family conflicts, listening to problems, or giving advice. Yet, he openly expresses envy over Natsuo's romantic experiences, often reacting with verbal complaints or playful physical holds. Fumiya harbors a longing for romance, particularly showing an attraction to older women. His personal hobbies include reading adult magazines and playing adult-oriented video games.

He works part-time as a waiter at Café L'Amant alongside colleagues like Masaki Kobayashi and Ayano. After high school, he pursues higher education at Tokyo University aiming to become a lawyer. Throughout Natsuo's complex relationships and emotional struggles—including those involving Hina and Rui Tachibana—Fumiya remains a steadfast source of counsel and refuge. His role persists as a reliable friend despite their evolving life paths.