It's a visual novel with elements of mystery and suspense, predominantly about the relationship between the Sheriff (Postman) and the Train Conductor (Gravekeeper). It's heavily based on the detective novel that is considered to be the inspiration behind the story of the Essence and contains spoilers for the original work. Additionally, the characters' backstories have been altered to better suit the story, and there are lots of headcanons and personal interpretations of these characters' original deductions.