Supreme Candy: Oudou ni wa Oudoutaru Riyuu ga Arun Desu! (2008)

Tonami Yuu is a somewhat awkward adolescent who keeps a certain distance between himself and others because of a traumatic incident that occurred when he was a child. One day he chances upon a jar of candy labelled 'Supreme Candy', a miraculous treat that allows him to change his physical age. Using this opportunity, he transforms himself into a child and enters the neighboring school's playground, where high school girls of his age play innocently with children. Yuu believes he has finally found something that will let him get close to other people again...