Sword Art Online (SAO) is a Virtual Reality Massively Multiplayer Online Role-Playing Game (VRMMORPG). With the Nerve Gear, a virtual reality helmet that stimulates the user's senses via their brain, players can experience and control their in-game characters with their minds. But when the players first log in to the game, they find they are unable to log out. They are then informed by Akihiko Kayaba, SAO's creator, that if they wish to be free, they must defeat the final boss. However, if their avatars die in-game, their bodies will also die in the real world. The story centers around Kazuto "Kirito" Kirigaya, who eventually befriends a female player named Asuna as the game progresses over the span of 2 years.