Kedamono ni Lollipop

Kedamono ni Lollipop summary:

Unlucky Himari Kawashiro, a shy and awkward high school student, only wants to be accepted by her peers. While trying to organize her school cultural festival without much luck, she accidentally stumbles upon a serious-looking cat eating cookies in an empty classroom. While fangirling over how cute it is, it transforms into her (now naked) classmate, Sennojou Shionji. He recruits her to be his sugar-toting assistant...and thus begins their odd partnership.