One day, Yoichi who grew up while not knowing his parents has received the news of his father's death. His father left behind a testament which said he is to pick only one out five little sister candidates.

I don't want to work, I want to laze around together with Onii-chan (By Serene).

Let's have a match. If I win, Nii-chan will make me his little sister. (By Tomomi)

Onii-chan will choose me, isn't that right. It's our destiny. (By Sayuri).

To be more girly, that why I want to be Nii-san's little sister. (By Yuuki)

If Mii-chan becomes Nii-chama's little sister, she will become rich right. (By Mika)

The little sister who were presented to him had more than one or two odd quirks, a slapstick comedy between siblings start here.

This is my first anime story but this not my story