Allegro, a vampire prince and secondary character, acts as Fine’s devoted caretaker, driven by unwavering loyalty and a determination to heal her while severing her ties to a painful past. This resolve intensifies when Fine escapes with Momo, a human he deems a threat to her stability, prompting his relentless pursuit. Bound by duty to vampire bishops tasked with upholding their bloodline traditions, he enforces strict norms, viewing human interactions through the lens of historical betrayal—a human once caused Fine profound anguish, cementing his hostility toward such alliances.

A skilled combatant, Allegro employs martial arts, acrobatics, and natural weaponry like claws and fangs. To amplify his prowess, he consumes a drug that triggers a transformative berserk state, granting heightened strength, flight, and agility at the cost of rationality. This duality mirrors his internal struggle between rigid duty and personal yearning to protect Fine.

His arc culminates in a fatal confrontation where a mortal wound sparks redemption. In dying breaths, he implores Momo to save Fine, abandoning tradition to prioritize her happiness—a fleeting glimpse of empathy beneath his austere exterior. Accompanied by his loyal dog Conny, Allegro embodies the clash between allegiance and self-determination, his journey underscoring themes of sacrifice and societal constraint. Vulnerable to ultraviolet light and lethal wounds, his existence mirrors vampiric fragility. Though initially antagonistic, his final act propels the narrative toward reconciliation, intertwining despair with fragile hope.