Knowing each other since their childhood years, the protagonist is like a little brother to the three sisters who live next-door. He is shy, and to fix this the second girl invented a cure drug. However, it went wrong and the protagonist becomes small! The three sisters loves him, and proposes to let him choose the one that will take care of him until he regains his previous figure.

This time, the eldest sister, Kasumi, looks after you. Beautiful and full of motherliness, she loves you unconditionally. Enjoy the child-making life with this gentle woman!