Board Thread:Suggestion Box/@comment-34434093-20180509212919/@comment-29759785-20180511050732

While I agree that she is not legally adopted (yet) and is it kind of silly to give her Kazuto's surname, "pretend" or "playing house" are also phrases I wouldn't use here. Both Kirito and Asuna are very dedicated to their role of raising Yui as their own child, and Yui, as far as she is able to understand it, treats them as if they were real parents. Even though not officially registered, the bond they have is surely on par with the real family.