The story begins with Yggdrasil, a popular online game which is quietly shut down one day; however, the protagonist Momonga decides to not log out. Momonga is then transformed into the image of a skeleton as "the most powerful wizard." The world continues to change, with non-player characters (NPCs) begining to feel emotion. Having no parents, friends, or place in society, this ordinary young man Momonga then strives to take over the new world the game has become.
(Summaries provided by MyAnimeList.net)