Ryunosuke Natsuke is a 14-year-old student living with his father Kyusaku and mother Akiko. His ordinary life shifts when the family shelters Atsuko Higuchi, a young woman discovered with amnesia. Unaware she is an escaped android prototype from Mishima Corporation, Ryunosuke develops romantic feelings for Atsuko, drawn to her beauty, gentle demeanor, and culinary skills as she integrates into their home.

He remains oblivious to her synthetic nature even as mysterious destructive incidents plague the town. Ryunosuke witnesses Atsuko's heroic alter ego, "Super Dynamite Girl," during these events but fails to recognize her.

His deepening emotional attachment to Atsuko becomes crucial when Mishima Corporation intensifies efforts to retrieve or eliminate her. During a critical confrontation where Atsuko initially cannot activate combat mode due to no perceived immediate human threat, Ryunosuke's arrival at the scene provides the necessary trigger, enabling her defensive capabilities.

The climactic conflict reveals Atsuko's origins as an android created by Professor Higuchi, alongside her lethal twin counterpart. Ryunosuke learns the truth about her identity and Mishima Corporation's involvement. His relationship evolves from a crush to accepting her dual existence as both a family member and a synthetic being.

Throughout the series, Ryunosuke transitions from a typical teenager into a supportive figure for Atsuko against corporate threats. His actions inadvertently influence pivotal moments, particularly his role in enabling her protective functions during confrontations.