Maerchen Ouji Grimm

Elementary school student Isobe Tatsuhiko has a crush on his classmate Shirayuki Yui. She seems out of his reach, however, since she's a gravure idol with the curves of a grown woman. One day, Prince Grim from the fairy-tale world shows up, trying to get Isobe to take his place and free him from the responsibilities of being a prince. To this end, Isobe's transformation into a fairy-tale person has begun! The only thing that will stop the transformation is to get a kiss of love from Shirayuki. But will Isobe be able to accomplish this with the meddling Grim still hanging around?

(Source: Mangahelpers)

Included one-shot:
Volume 2: Märchen Ouji Grimm (one-shot version)