Nagi Umino, born to the wealthy Amano hotel proprietors but accidentally raised by the Umino restaurant family, discovers his true lineage upon meeting Erika Amano—the biological daughter his parents raised. To maintain ties with both children, their families arrange a marriage between Nagi and Erika. Though initially resistant, they eventually cohabitate in an Amano-owned residence. Physically, Nagi sports short black hair, blue eyes, and pale skin, typically dressed in his Megurogawa Academy uniform: a white dress shirt and black pants. Academically driven, he relentlessly pursues top rank at school to secure scholarships and ease his adoptive family’s financial burden. Highly proficient in household chores, particularly cooking—often preparing meals influenced by his family’s restaurant—he exhibits stubborn determination and protectiveness toward loved ones. Yet he remains romantically naive, avoids conflict, and habitually prioritizes others over himself. Romantically, he initially crushes on Hiro Segawa, the grade’s top student, vowing to confess after surpassing her academically. They date briefly after he achieves first place in midterms, but Hiro ends the relationship over long-term incompatibility. Concurrently, he develops feelings for Erika, his arranged fiancée; they eventually confess mutual love, though his relationship with Hiro causes Erika distress. His adoptive sister, Sachi Umino, develops romantic feelings for him upon learning they are not biologically related. His childhood friend, Ai Mochizuki, also harbors longstanding romantic affection. Character development sees him evolve from a logical, headstrong youth to someone increasingly indecisive in romance. He acknowledges hurting Erika by choosing Hiro and later commits to her by confessing his feelings to her father. He navigates complex familial bonds, maintaining a protective dynamic with Sachi while persistently searching for his biological older brother, Sousuke Amano. Beyond academics, he excels in cooking—adapting restaurant recipes to impress others—and demonstrates physical strength when defending Erika from stalkers. However, he struggles with sports and displays social awkwardness, such as maintaining a stoic expression in photos. Trivia notes include susceptibility to seasickness, an Aries zodiac sign, and an inadvertent habit of nudism at home when alone, leading to comedic mishaps. His name, meaning "calm" or "lull," contrasts with Erika’s outgoing nature.