Sword Art Online, light novel Vol. 09: Alicization Beginning

Kirito awakens in a vast, fantastical forest filled with towering trees. In his search for clues to the truth of his surroundings, he encounters a young boy who seems to know him. He ought to be a simple NPC, but the depth of his emotions seem no different than a human. As they search for the boy's parents, Kirito finds a peculiar memory returning to him. A memory from his own childhood, of this boy and a girl, too, with golden hair, and a name he should have never forgotten--Alice.