Kazuki Kurusu is a professional assassin in his late twenties who operates with his partner Rei Suwa. His expertise spans intelligence gathering, mission planning, and contract execution. Physically, he has untidy mid-length blonde hair, tanned skin, a slim face, and a slender but well-built frame standing around 6 feet (184 cm). For assignments, he typically wears an off-white shirt, red hoodie, knee-length dark green coat, navy blue pants, and brown sneakers. At home, he dons casual clothes with a blue apron featuring a shark print. Charming and verbally adept, Kazuki battles irresponsibility fueled by gambling temptations and romantic pursuits with women. Despite these flaws, he shows deep loyalty to loved ones. He struggles with improvisation and deception during mission disruptions—Rei labels him a "lousy actor." Emotionally expressive, he contrasts Rei's stoicism, often overreacting dramatically to family-related stress. As a homemaker, he excels at cooking and cleaning, frequently scolding Rei for messiness. Orphaned without knowledge of his biological parents, Kazuki married Yuzuko Kurusu while she was pregnant. During one of his missions, a fleeing target triggered a gas tanker explosion that killed Yuzuko. Consumed by guilt, he sends money to her sister Karin Izumi as penance, though Karin refuses it, insisting he bears no blame. This tragedy cemented his belief in his unfitness for parenthood. His life shifts when he and Rei encounter four-year-old Miri Unasaka at a mission hotel. After Kazuki accidentally prompts Miri to call him "Papa," they assassinate her biological father—their target. Learning Miri was abandoned by her resentful mother Misaki, Kazuki resists keeping her but gradually embraces fatherhood. He forges documents to enroll her in daycare, adapts to childcare, and grows fiercely protective. When Misaki reclaims Miri only to be murdered, Kazuki and Rei adopt Miri, abandon assassination, and build a legitimate family abroad. Kazuki evolves from a guilt-ridden, commitment-averse man into a devoted father. He transitions from anonymous payments to Karin to openly prioritizing Miri’s welfare, confronting his parental fears. His bond with Rei deepens into familial partnership as they co-parent Miri, becoming "Kazuki-papa" and "Rei-papa." A decade later, he retains his emotional, protective nature, though persistent traits like womanizing sometimes clash amusingly with Miri’s maturity.