Sword art online

Sword Art Online (SAO) is an anime about a virtual reality video game where all the players get stuck in and they have to win to free themselves out of the game. If they die in the game, they die in the real life. Kirito is its protagonist and he's a sixteen-year-old boy who's very good and strong and he finally wins the game but sacrificing himself for the sake of the players and to revenge the death of his girlfriend, Asuna.