Rei Suwa is a 25-year-old professional assassin raised within a criminal family organization. Trained from childhood under abusive conditions by his father, including combat drills involving being chased by dogs, this upbringing left him emotionally scarred and incapable of understanding conventional parent-child relationships. His father openly rejected their biological connection, viewing him solely as a weapon. Physically, Rei possesses indigo blue eyes and medium-length black hair. He often wears it unstyled and loose casually but ties it in a high ponytail during missions, revealing previously shaved sides. His appearance conveys intimidation, accentuated by perpetually shadowed eyes. For work, he wears formal suits with gloves; off-duty attire consists of a blue jacket, dark shirt, and jeans. His personality starkly contrasts between professional and personal settings. As an assassin, he demonstrates exceptional tactical skill, marksmanship, and emotional detachment, eliminating targets efficiently. Outside work, he adopts reclusive tendencies, spending hours playing video games in darkened rooms with minimal communication or eye contact. He exhibits childlike behaviors, preferring sugary foods over nutritious meals, neglecting basic self-sufficiency like heating dinner, and relying entirely on his partner Kazuki Kurusu for domestic tasks. Notably, he sleeps in a bathtub as a security precaution against ambushes. Rei’s relationships evolve significantly through co-parenting Miri Unasaka, a four-year-old girl whose father they assassinated. Initially distant and avoiding interaction, Rei gradually accepts a paternal role. A turning point occurs when he prevents police from taking a lost Miri, explicitly claiming her as his daughter to protect her. This contrasts his own father’s cruelty and reflects his growing commitment. He bonds with Miri over shared interests like gaming and exhibits concern during her illness, though his expressions remain reserved. His partnership with Kazuki deepens from functional coexistence to profound loyalty; Kazuki is his sole friend and emotional anchor. Rei eventually confesses his love for both Kazuki and Miri, willing to sacrifice his assassin identity for their safety. Character development culminates when Rei confronts his father, rejecting the assassin legacy to protect his found family. This decision leads to a physical altercation resulting in permanent injury, symbolizing his break from the past. In the epilogue set years later, he lives overseas with Kazuki and Miri, having abandoned crime for a legitimate life. His appearance softens with a low ponytail and unshaved sides, reflecting his transformed identity as a dedicated co-parent.