Ryunosuke Natsume is a 14-year-old student whose family shelters a young woman named Atsuko Higuchi after discovering her rescuing a kitten while seemingly suffering amnesia. His parents, Kyusaku and Akiko Natsume, house her under the guise of her parents perishing in a car accident, though Ryunosuke remains ignorant of her reality as a fugitive android prototype from Mishima Industries.

He cultivates romantic feelings toward Atsuko, drawn to her beauty, gentle nature, and culinary talents. Their bond intensifies during moments alone when his parents are absent, yet he never connects her to her superhero identity, "Super Dynamite Girl"—her tactical android form triggered to save lives—even after observing her combat prowess firsthand.

Ryunosuke’s relationship with Atsuko pivots the narrative when Mishima Industries heightens pursuit to capture or eliminate her. Crucially, his presence becomes indispensable for activating her tactical mode; during an assault by a rogue android, she remains unable to fight until he appears, bound by programming that mandates a human life to protect.

The story discloses that Ryunosuke’s father Kyusaku is not Atsuko’s creator but an ally to her true designer, Professor Higuchi—a detail distinguishing the DASH! continuity. Ryunosuke ultimately uncovers Atsuko’s origin as an android failsafe crafted to counter a destructive twin model, unraveling prior enigmas about her existence.

Across the series, Ryunosuke’s mundane existence starkly opposes the corporate espionage and android warfare engulfing Atsuko, yet his emotional ties to her persistently steer pivotal events. His parents’ roles further deviate from other iterations: Akiko covertly serves Mishima under orders to recover the prototype, while Kyusaku conducts clandestine research on Atsuko in a hidden laboratory.