Otokonoko Mahou Shoujo no Ecchi na Maryoku Hokyuu

The main character, a boy who accidentally becomes a magical girl, spends his days fighting evil monsters that bring misfortune to people.
One day, the main character goes to the house of another male magical girl to replenish the magical power he used up in the battle with the monsters, but there he learns that the male magical girl's way of replenishing her magical power is by cross-dressing... That's the story.

(Source: Melonbooks )

Note: Released at Comiket 106