Road to Forest is a recurring area from the original game.
It's only accessible the first time entering the door beyond the Henkei Shita.
The area is one long street surrounded by trees, with one Floyag seen in the background. It's raining constantly.
Onsen-san sits in the middle of the street, blocking Madotsuki's way. Killing it with the Knife effect causes it to seemingly transform into Shitai. Madotsuki will wake up after that, disturbed and regretful.