What's the deal with Yui? I've watched all the episodes on Crunchy Roll (SAO and ALO) and I think I missed something.

The character Yui acts as though she is the child of Asuna and Kirito.  I do not remember Yui in the SAO arc, but perhaps I missed it.

When did Asuna and Kirito have a child?  How did that child get special access to the system?
Yui is certainly a part of the SAO arc - she appears in it quite prominently.

She is found by Kirito and Asuna and they "adopt" her in SAO, though she turns out to not be exactly what she appears to be.


   She is, in fact a program. A mental health assistance program (who has been disallowed from doing its job when SAO was locked down). This explains her special system access and knowledge.