Amakawa Haruto, a Japanese university student, perished in a traffic accident with Minamoto Rikka and Endo Suzune, reincarnating as Rio, an orphan in the Beltrum Kingdom’s slums. In his previous life, Haruto formed a deep bond with childhood friend Ayase Miharu in a metropolitan city. Following his parents’ divorce, he relocated to a rural area, devoting himself to martial arts to honor a promise to return and marry her. His unresolved guilt over losing contact before her disappearance during a hero summoning event lingered until his death at twenty. Reborn as Rio, he endured a childhood shadowed by his mother’s murder and enslavement in the slums. At seven, Haruto’s memories resurfaced, merging their identities. This fusion granted maturity, martial prowess, and a vengeful purpose: to hunt Lucius Orgueil, his mother’s killer. Survival in the slums left physical scars and forged a guarded, solitary nature. Admission to Beltrum Royal Academy followed his rescue of Princess Flora, yet his commoner status invited relentless noble disdain. Excelling academically and martially through Haruto’s knowledge and spirit arts training, he topped rankings, fueling aristocratic animosity. Framed for regicide, he fled as a fugitive. Wandering lands, he saved Latifa, a beastkin assassin, allied with spirit folk, and honed spirit arts to craft enchanted gear. A journey to Yagumo unveiled his royal lineage as the Karasuki Kingdom’s lost prince, reconciling his dual existence. Rio wields mastery of ancient martial arts, swordsmanship, and spirit arts amplified by his contract with Aishia, a high-class spirit. Their bond enables assimilation, summoning spirit weapons and unleashing transcendent powers like Annihilation—erasing targets from existence. Mythril blades, a space-time cache, and an identity-concealing hair artifact aid his combat, shifting his black hair to silver or white during spirit fusion. Haruto’s inherent kindness and loyalty merge with Rio’s survival-driven pragmatism and self-doubt. He fiercely protects allies but battles guilt over vengeance corrupting his connections. Bonds with Celia Claire, Miharu, and Latifa gradually thaw his emotional walls, teaching him to accept kinship. His resolve to shield loved ones from danger weakens when facing foes like Lucius and Sakuraba Erika, forcing nuanced choices between compassion and lethal justice. Pivotal moments include reconciling Rio and Haruto’s identities, embracing his destiny as the Dragon King reborn, and maneuvering through cross-kingdom political schemes. Reuniting with Miharu and encountering other reincarnated souls like Liselotte Cretia forces reckoning with past failures and future duties. Harnessing divine authority, Rio now prioritizes shielding his chosen family while seeking closure on vengeance, redirecting his path from retribution to protection.