sayori.chr is a file that's present in the
characters folder of the game directory. It's an OGG audio file without any discernible meaning. However, the spectrogram of the audio file reveals a QR code. When scanned, it leads to http://projectlibitina.com/.
No significant relations between Sayori and Project Libitina have been found. Possibly of note, however, is the fact that Sayori's poem % has the same title as the document present on the website, though this could be coincidence.