Anger

That was what he felt when Kayaba Akihiko imprisoned him in the game.

When the Black Cats of the Night was dying in front of his eyes.

When he saw The Gleam Eyes attacking his friends.

When he was about to die from Kuradeel.

When Yui died because she was a foreign object.

When he fought Kayaba Akihiko, who had even killed Asuna.

When it was just a little distance away to enter the Tree of Life.

When he watched Sugou playing with Asuna's body.

When he was in desperation, grief and frustration.

There was Kirito's anger.