If you look up the songs, you'd realize you've heard them before. Especially Habanera (the song that goes "param pam pam" hahaha)and Satie's pieces. Also i recommend you listen to the Sleigh Ride Duet by Frank and Zach on youtube. It gives off the perfect atmosphere for the chapter about the Christmas Concert and explains perfectly Isshilki's expression at that time. (⌒▽⌒)
If you look up the songs, you'd realize you've heard them before. Especially Habanera (the song that goes "param pam pam" hahaha)and Satie's pieces. Also i recommend you listen to the Sleigh Ride Duet by Frank and Zach on youtube. It gives off the perfect atmosphere for the chapter about the Christmas Concert and explains perfectly Isshilki's expression at that time. (⌒▽⌒)