One morning, Eri ran up to her two fathers, Hizashi and Aizawa

Eri: Dad? Papa?

Aizawa: Yes, Eri-chan?

Eri: I feel really lonely…

Hizashi: Lonely..?

Eri: I want a sister!

Hizashi: But haven’t you already got Shinsou?

Eri: He’s boring! Can’t you make me a sister? Like… ooh! A robot sister!

Aizawa: Robot..?

months later, the robot was nearly complete. Aizawa and Hizashi were putting the finishing touches on the robot. Shinsou and Eri walked in

Eri: Is she done?

Hizashi: Almost!