251230 ‘No Way Back (THE SIN : VANISH Chapter 1)’ has been uploaded on Spotify, revealing that the track features So!YoON!

Apple Music had uploaded the music video of the album teaser which mentioned this as well! I had posted a comment earlier but then decided against it.

https://preview.redd.it/cwwdtepz6aag1.jpeg?width=1170&format=pjpg&auto=webp&s=123e994ea0c8258cc80843099a342081446153a2