I was designed to put players at ease with me.
That's why I was given the ability to emulate complex emotions.
Nothing about me is real. Nothing... Not even my tears.
I'm so sorry, Asuna...

Yes. Kirito. Asuna.
Everything in the world of Sword Art Online is controlled by a single massive system.
The system is called Cardinal.
It was designed to operate entirely on its own without any human intervention.
Its function is to regulate the balance of SAO according to its own discretion.
From monsters and NPC AI to drop-rates for items and money.
Everything here's controlled by the processes the Cardinal program executes.
That includes the psychological care of players.
Mental Health Counseling Program, prototype one -- code name: Yui.
That is who I am.

Two years ago, on the day of the official launch, and for reasons I never understood, the Cardinal program banned me from interacting with any of the players.
I wasn't allowed to assist them.
I couldn't do anything except continue monitoring their mental states.
Their situation, in a word, was horrible.

No, don't!

Terror, despair, rage. People were overcome by negative feelings.
Some of them couldn't take it. They went insane.
Under normal circumstances, my function would've been to go to such players immediately.
But I wasn't permitted any contact with them.
Little by Little, errors began piling up inside of me, and I fell apart.
Then one day, I saw two players.
Their mental parameters were vastly different from anything I'd seen among the others.
There was joy... and peace. And there was something more.
I wandered through the playing field, hoping to get as close to both of you as I could without being detected.