Magic User: TRPG de Sodateta Mahoutsukai wa Isekai demo Saikyou Datta.

A man in his forties, who was once a tabletop RPG fanatic, has settled into the ordinary job (and life) of a salaryman. All of that changes when he’s tossed into a parallel world by a mysterious entity and finds himself in the form of Gio Margilus–his max-level wizard character from the classic tabletop RPG Dungeons & Brave! Roll the dice with this new isekai light novel series for gaming fans, both new and old.

(Source: Seven Seas Entertainment)