Looking for anime forgot the name?

StormJumper

I am not sure of a anime I have or seen but here how it goes.

She is elementary school but has the looks and body of a high school girl and her cousin he is high school but she is tall just like him. And her living with him makes it a odd living situation. He finds her attractive but she is still elementary student and he is high school student. It's not Cyclops Shoujo Saipu. But the characters are similiar drawn.

Quirk

Go to myanimelist.com and search for it. I don't know the anime myself.
Maybe it is even the same mangaka?
If you check Cyclops Shoujo Saipu, there should be recommendations based on similarities. So chances are your anime will compared to Cyclops.
When you say elementary school do you mean middle school? Otherwise she would be under 12.