The whole AI thing is just a bit too unbelievable for me. That, and the fact that she was downloaded into the nerv gear headgear. I also simply dislike cutesy shallow characters like her. I know she is AI and that cannot allow for much development, but weren't they selling her character as something more, almost human perhaps? Her role in the fairy arc was even more of a stretch. All of a sudden, she is recognized by the system as tinkerbell, and can get all sorts of information despite being a foreign object. All we get are one liner explanations, and really, she does nothing for the plot.

It's like they wanted to add a constant loli that won't attract Asuna's wrath, so Yui suddenly got inserted into the story.

Almost insignificant spoiler for the coming Gun Gale Online arc:





Almost no Asuna or Yui.