Koichi Mizuki, a Japanese high school student and championship-winning captain of his school's basketball team, balanced athletic excellence with top academic performance. Personal loss marked his childhood: his father died when he was three, and his mother later succumbed to overwork during a business trip, leaving his uncle as his sole known relative. Physically, he possesses tan skin, brown eyes, and short black hair styled with outward spikes at the top, reaching his ears. A heart-shaped mark appeared below his stomach after forming a contractual bond with Caius, a prince from another world, granting Koichi limited access to Caius's magical abilities. His personality blends tenderness and warmth with a strong-willed resistance to decisions made without his consent, exemplified when he intervened to stop Caius from killing his kidnapper, Palo, declaring he wanted no harm done on his behalf. His summoning to the world of Tildant occurred unexpectedly during a private moment at home, placing him among giants. Initially frightened and resistant to Caius's proposal to become his bride, Koichi negotiated a one-month trial. Caius agreed to refrain from non-consensual acts and to return him home if he chose to leave. Over the month, Koichi gradually adapted to the giants' culture, which openly embraced diverse relationships and sexuality, leading him to develop genuine affection for Caius. He ultimately chose to remain in Tildant, accepting a magical contract that erased his existence from his original world. This resolved dimensional instability caused by the summoning but permanently removed him from his former life. Key relationships include his evolving bond with Caius, transitioning from fear to deep commitment; initially tense but later amicable interactions with Medina, Caius's former fiancée; and a complex dynamic with Palo, whom he forgave after the kidnapping. He maintained a cautious friendship with Jin, thanking him for aid during a severe illness. Before his summoning, he held a potential romantic interest in a female classmate, Anzu Tanaka. In expanded media like the game *Gyee*, he appears as a dimension traveler. His combat abilities leverage his basketball skills, featuring projectile attacks named "Shoot" and "Mana Projection," plus an ultimate ability called "Tildant Blessing" reflecting Caius's protective influence. This story continuity begins when touching a Longears' treasure caused both him and Caius to lose consciousness and reappear in a new realm. His development includes undertaking culturally significant tasks in Tildant, such as attempting to hatch a stillborn egg for the Hubbard royal family—an effort others deemed impossible, demonstrating his determination to integrate. His journey consistently engages themes of consent, cultural adaptation, and emotional resilience.