Kuroto Hōrai, the youngest Zweilt guardian, possesses black hair and striking golden-green eyes. He initially trained as a professional shogi player, a passion fostered after being taken in by Senshirou Furuori's grandfather. He ultimately abandoned this career path to dedicate himself wholly to fighting the Duras, believing both pursuits demanded his full attention. Serious and reserved, Kuroto often appears closed off, having once viewed life as a solitary journey. Despite his quiet exterior, he experiences intense emotional reactions, especially to negative events. He exhibits a tsundere nature, becoming easily flustered and embarrassed by compliments, particularly those from Senshirou; he typically responds with anger or by telling him to shut up. Senshirou calling him a "good kid" visibly agitates him. While sharing a similar demeanor to Luka Crosszeria, Kuroto expresses emotions like vengeance more overtly. Significant trauma marks his past. Brought to Senshirou's family dojo at age seven for training, he had resigned himself to solitude after losing his original partner Oboro in a past life. The demon Cadenza attacked the dojo, killing Master Garan and others. Kuroto and Senshirou survived only because Garan erected a protective barrier before the battle. This cemented Kuroto's hatred for Cadenza, who killed both Oboro and Garan, fueling his relentless quest for revenge. Relationships shape his development. His bond with Senshirou evolves from viewing him as an "idiot" to deep reliance, though Senshirou's attentiveness, likened by others to a "man-servant," easily embarrasses him. Initially distant toward Yuki Giou, Kuroto gradually warms to him. Rediscovering his enjoyment of shogi through their matches leads to a monthly playing habit. He once attempted to welcome Yuki home after a trip, blushing and becoming irritated when Senshirou spoke first due to his own shyness. He respects Luka Crosszeria, acknowledging a debt for saving his and Senshirou's lives. In combat, Kuroto wields the black katana Izanagi (Hell). As a Zweilt without innate supernatural abilities, his power stems from dedicated focus on swordsmanship. Personal quirks include a fondness for Japanese sweets; he once abandoned his usual restraint to angrily confront thugs who knocked his ice cream to the ground. His development centers on emerging from self-imposed isolation, influenced by Senshirou's unwavering presence and Yuki's kindness. Though his drive for vengeance against Cadenza persists, he demonstrates the capacity to prioritize, setting aside revenge to aid in Yuki's rescue. His journey reflects a shift from solitary determination toward acknowledging interdependence with his allies.