PTSD Radio manga volume 2 contains volumes 3-4 in an omnibus format and features story and art by Masaaki Nakayama.

When you bend over the bathroom sink, you can't see what's behind you in the mirror. A gaping maw with too many teeth drags itself toward you up the stairs.

Skit skit skit. What's that crawling in your mouth while you sleep? Next, it wriggles its way into your ears, your nose, your brain...

Learning the origin of Ogushi-sama may help you find the answers you seek.