Boku Girl

Boku Girl (ボクガール) is a 2013 manga serieswritten by Sugito Akira and is serialized in Shuukan Young Jump. It has a side-story under the name Boku Girl: Boku no Arbeit.

Plot
Mizuki gets confessed to by a boy in front of a special Mirror. Loki decides out of boredom to mess with Mizuki and turns him into a real Girl.

Other Sources

 * https://www.mangaupdates.com/series.html?id=105986