Sword Art Online: Alicization

Kazuto Kirigaya gets attacked and suffers brain damage. In order to save him and at the same time further his own project at Rath, Kikuoka Seijirou puts Kazuto in a STL (Soul TransLator) machine. Kazuto ends up as Kirito in a new world called Underworld. He befriends a boy called Eugeo and together they try to save a girl named Alice who was taken from Eugeo's village years ago.