Chihaya Hiiragi, a high school student balancing shifts at her family’s restaurant Angel Kiss, discovers her destiny when Natsuki—a rabbit-like envoy from the parallel realm Evergreen—bestows her with transformative powers. As Magical Warrior Carmein, she adopts an idealized adult form, wielding enhanced magic to combat threats born from corrupted magical seeds that prey on human longing.

Her dual identity contrasts gentle everyday kindness with Carmein’s bold, self-assured demeanor, mirroring her hidden ambitions. Transforming requires Natsuki’s aid, though their partnership fluctuates between tense camaraderie in the original OVA and cooperative rapport in the anime adaptation.

Tasked with neutralizing seed-spawned monsters, Chihaya clashes with Cerulean Blue, a rival warrior, and allies with figures like Septem—an Evergreen exile who transitions from OVA antagonist to TV series confidant. Familial ties further complicate her journey: her father Bergamot, a fugitive from Evergreen, emerges to shield her from foes like Fennel, who covets her latent powers.

The "Summer Camp" OVA expands her trials through a seaside escapade with classmates, pitting her against the Netherworld Tree alongside Nami Minami, a peer entangled in supernatural chaos. Visually, her civilian identity pairs a school uniform and beret with youthful charm, while Carmein’s sleek qipao-inspired battle attire, adorned with arcane ornaments, accentuates her empowered physique. Across adaptations, her story weaves the struggle to reconcile mundane obligations, magical duties, and the legacy of her lineage amidst Evergreen’s encroaching shadows.