In the near future, a Virtual Reality Massive Multiplayer Online Role-Playing Game (VRMMORPG) called Sword Art Online has been released where players control their avatars with their bodies using a piece of technology called Nerve Gear. One day, players discover they cannot log out, as the game creator is holding them captive unless they reach the 100th floor of the game's tower and defeat the final boss. However, if they die in the game, they die in real life. Their struggle for survival starts now...

Eiichirō Maruo (nicknamed "Ei-chan" for his grades being straight "A") is an honor student, bookworm, and is not interested in anything other than studying. In order to solve his problem of lacking physical strength, he enrolled a tennis school and soon found the fascinating side of tennis. Being a tennis newbie lacking physical strength, he supplement his shortcomings with his excellent observing and analyzing skills.