Shinichirou and his sister Kotomi discover a mysterious android girl named Arisa who has fallen from the sky. Although Arisa claims to be a perfect domestic helper, she is incredibly clumsy, leading to a strained relationship with her new master. The household's dynamic shifts when they hire Yuuri, a student who is secretly a soldier searching for a weapon known as "Fire Bee." After mistakenly targeting Kotomi, Yuuri realizes that the useless and cheerful Arisa is actually the advanced military android she has been hunting.
Shinichirou's peaceful life is shattered when the villainous Ryugasaki kidnaps Saya and Yuuri to blackmail him into surrendering Arisa, the secret weapon known as Fire Bee. With the help of his grandfather, Shinichirou learns the truth about the electric dolls' origins and encourages Arisa to fight for her friends. Transforming into her powerful combat form, Arisa raids a secret military base and battles the incomplete Fire Dragon to rescue her family.