Here, in a map called the "Burning Room"--in the center of that cluster of figures in the bottom right corner. I'm having a bit of difficulty pinpointing exactly where one of preceding areas connects to. It's also listed in the database as an effect.
EDIT: I managed to find my way to the area and obtain the effect! It requires Usotsuki to fall asleep in a particular iteration of the train car interior. Since it requires 100 currency per ride, I suppose the Nail Bat is needed (or you can gather money but that would take time). The Match effect is also required to reveal the NPC that gives it.