Kiriko Kiyuna, a former pilot of the combat robot Daimidaler, retired following the dissolution of her organization but remains a high school student defined by her earnest purity. She reciprocates the romantic feelings of Shōma Ameku, whose confession deepens their bond. This relationship fuels her Hi-ERo particles—critical for powering Daimidaler—through intimate moments that frequently escalate into public affection, drawing reprimands from faculty. Uniquely capable of summoning Daimidaler remotely, Kiriko leverages this skill when Shōma is transformed into a penguin and coerced into serving the Penguin Empire. Undeterred by his temporary absence, she fiercely commits to his rescue until external allies restore his humanity, reuniting them.

Her path intersects with Kōichi Madanbashi, a fellow student distinguished by his irregular uniform and notoriety. Though initially withdrawn from conflict post-retirement, Kōichi’s apparent death reignites her resolve, thrusting her back into battle as a pivotal adversary against the Penguin Empire. Throughout, Kiriko grapples with harmonizing her devotion to Shōma with her duty to confront larger threats, embodying unwavering loyalty and tenacity in both love and combat.