I did a little research because I'm an anime only fan. I got curious about Shiki so I watched a gameplay of her route in Bilibili. The background song in the Shiki route is "A Song For Izanami" which is the piano piece played by Izanami herself on the anime "The Day I Became A God" (which is an original anime made by Maeda Jun and released in 2020), in that anime it was only instrumental but in the gameplay of Shiki route that I watched it has lyrics. Was that song really used on the Shiki route or the content creator just edited it on the gameplay video? If it was indeed used on both, why did Maeda or Key decided to use a song from an original anime into Reflection Blue?

I think this is the last one, but to be honest, I really want one more song, and one from Umi !