An extraordinary being, Sonnet, a cyborg with esper abilities, emerges from a tumultuous past, honed into the ultimate warrior and a formidable weapon. Tasked with monitoring Komatsuzaki Lan in Japan, believed to be influenced by the vengeful esper Akai Kiba, Sonnet's encounter with Lan sparks a transformation. Lan, a reserved girl grappling with her uniqueness, begins exhibiting traces of Crimson Fang under Sonnet's watchful eye. Through their clashes, Sonnet embarks on a journey to reconnect with her human side, while Lan fights to preserve her humanity and tame the powerful Crimson Fang lurking within.