She Professed Herself Pupil of the Wise Man Kenja no Deshi wo Nanoru Kenja

Kagami Sakimori plays as the great mage Danblf in his favorite MMO. He falls asleep after a night of testing new character appearances, but instead of waking up to a suspended game, he’s inside of Arch Earth Online—as a girl! Now named Mira, he must convince the game’s people that Mira is a pupil of Danblf, who vanished without a trace 30 years ago…and figure out how he got here.

(Source: Funimation)