As Yui was originally a girl without her memories, she felt insecure about not knowing who or where her "parents" were, so she assumed that Kirito was her father and Asuna was her mother. After the couple decides to play along as the girl's parents due to the girl's psychological condition, she begins to be very cheerful and shows great affection for her so-called "parents". According to Asuna, her behavior was like that of a baby, despite her young appearance. However she does not show any fear, regardless of the kind of danger she might be in and even shows signs of rebellion when Kirito tells her that she has to stay with Sasha when Kirito and Asuna wanted to go to a dungeon to rescue Thinker.