>>527999080
>>527999016
Ralsei recognizes Rouxl's theme if you play it on the piano.

Also, if you play the Dark Sactuary music on the piano, Susie goes "hey I recognize that", which causes Ralsei to get confused, and then Susie says that she heard Ralsei humming it earlier.

So at the very minimum, Ralsei can hear the music for some reason, but it doesnt seem like Susie can.