Basically once upon a time I was reading a manga. The main character was overweight, and basically had inhuman strength. She also had a whole summer I think of time missing in her memory that something super important happened. She gets two friends(sort of) one is a younger girl who wants to be just like the heroine and the other is her "greatest rival" a former leader of a school gang who was easily defeated by the heroine and now trains to beat her Any help would be greatly appreciated.

Should be this one: Metsuko ni Yoroshiku by COOL Kyoushinsha. All his series take place in the same universe, and there are a few cameos across his series.

Yesh thank you! awesome.