GM ga Isekai ni Login Shimashita.

Toudou Masaki works as a Game Master on his favorite MMORPG, Britalia Online. There might be strange rumors circulating about players disappearing and his job might force him to pull one all-nighter after the other, but Toudou is pretty content with his life. That is, until he suddenly loses consciousness during a break one day. When he wakes up, he finds himself involuntarily summoned to a whole new world where magic, in-game skills, and monsters are part of the daily grind. Fortunately, Toudou quickly discovers that he still has access to his Game Master abilities, and he fully intends to make use of every means at his disposal to survive in this world ravaged by war. But first, he needs to escape from his cell... Follow the adventures of Toudou as he makes use of his overpowered GM abilities to battle his way through mobs galore! (Source: J-Novel Club)