She Professed Herself Pupil of the Wise Man - OP

Going by the name Dunbalf, he’s known across the land of this virtual world. But one night before bed, Kagami uses an in-game vanity case that’s about to expire—opting to create his ideal version of a female Dunbalf avatar for fun.

Waking up, he’s surprised to find that he’s now in the body of the avatar he created the night before, and he’ll have to work his way from the bottom up! So he’s a young dude, playing an old dude, who is now playing a young girl—who is still that old dude.