Sword art online

Kazuto Kirigaya, aka Kirito, dives back into the virtual reality game "ALfheim Online" to save Asuna, who has not regained consciousness, and he meets a girl named Leafa, who decides to help him in his quest. Unknown to both of them, however, is the fact that Leafa is Kirito's real life sister and, even in the game, she instinctively needs to help and protect him.