No premiere date announced yet. The new PV is here. Check out the ANN article for additional information. Synopsis for the source novels from AniList:

A mysterious door stands open, inviting a boy who’s been brutally bullied all his life to take a courageous step forward into the unknown. On the other side, he finds a hoard of priceless artifacts and a world as filled with magic as it is with monsters. The most shocking revelation, however, is that he can bring whatever he wants back with him when he returns to Earth. It won’t be long before this double life changes him forever…