Chen Muxue reasonably suspected that the "ghost" in this Illusion Realm might also be based on Xiao An's memory. It's even possible that this time, the protagonist in the Illusion Realm isn't the Black Cat itself, but rather the girl in front of her named Xiao An...
What does Xiao An represent in the Black Cat's life? Chen Muxue doesn't understand the Black Cat's life, and she has no way to guess.
However, judging from Xiao An's attitude, Chen Muxue should protect her. She's the only kind person Chen Muxue has encountered in this Illusion Realm.
According to Chen Muxue's guess, the Illusion Realm should be a manifestation of regrets and obsessions. Since Xiao An is the protagonist in Black Cat's Illusion Realm, perhaps Black Cat's regret lies with Xiao An.
