Takuma Sakamoto is a hikikomori gamer who is mysteriously transported to the world of his favorite MMORPG, Cross Reverie, with the appearance of his own character in the game, the Demon Lord Diablo. The two young girls who summoned him, the pantherian Rem and the elf Shera, attempt to use a spell to make Takuma their servant, but due to his passive “Magic Reflection” ability, the spell rebounds, and both end up with magic collars stuck on their necks, thus becoming his slaves instead. With a serious case of social anxiety, Takuma decides to act like his character while interacting with others, and makes use of his high stats and vast knowledge of Cross Reverie’s lore to survive in his new environment, traveling along with Rem and Shera to look for a way to remove their slave collars while helping them with their own, personal issues that led them to summon him in the first place.

In the year 2126, a Dive Massively Multiplayer Online Role-Playing Game or DMMORPG called Yggdrasil was released. It stands out among all other DMMORPG’s due to its unusually high ability for the player to interact with the game. After an intense 12-year run the game servers are about to be shut down. Within the game exists a guild, Ainz Ooal Gown, once consisting of 41 members and credited as one of the strongest guilds in the game. Now only 4 of the members remain, the other 37 having quit the game. Of those 4 only one, an elder lich character named Momonga continues to play as the guild leader and maintaining their headquarters, The Great Tomb of Nazarick. He invites the remaining guild members but of those only one appears and only for a short while before leaving. While saddened by this, he accepts the reality that his friends have their real lives to take care of and decides to stay logged in until the servers shut down.

When the shut-down time arrives, however, Momonga finds that the game hasn’t vanished. Instead, it appears as if Yggdrasil has been recreated as its own reality along with its various NPCs having been brought to life while Momonga has been trapped in the form of his game avatar, leaving him unable to use the normal player functions, such as General Message, or even to log out. With no other option, Momonga sets out to learn if anyone from ‘the real world’ is also in this new world with him. Taking on the name of Ainz Ooal Gown, a message to any other players, Momonga begins exploring the world in an attempt to figure out what has happened while searching for anyone, or anything, that could help him solve this mystery while ensuring the safety of Nazarick.

In a world of fantasy, adventurers come far and wide to join the Guild, in order to complete contracts for whatever jobs are available. An inexperienced priestess joins her first adventuring party but comes into danger after her first adventurer contact involving goblins goes wrong. After the rest of her party is wiped out, she is saved by a man known as Goblin Slayer, an adventurer whose only purpose is the eradication of goblins with extreme prejudice.