Aoki Genu (voiced by Hikasa Yoko) is a very ordinary first-year high school girl. One day, she received a mysterious package. After unpacking it, a small robot named "Frame Arms Girl" appeared in front of Aoki. Honglei is not an ordinary robot. She has her own consciousness and can continuously evolve by learning human emotions and fighting methods. In this way, Aoki and Honglei's cohabitation life began. In addition to Honglei, there are other mecha girls. The tsundere (voiced by Ayase Yu), the simple-minded Shanyan (voiced by Changjiang Riga), the carefree but full of justice Xunlei (voiced by Kabayama Nan), and the emotionless and taciturn Bone Princess (voiced by Yamamura Hibiki), after Honglei, they appeared one after another beside Aoki.