Research Paper On Noppera-Bō
Noppera-bō will appear as your average toilet pervert but with the added creepiness of having no face, just a smooth featureless slate.* He often appears in woman's restrooms but luckily he's more of a mischievous spirit than a deadly one. Noppera-bō is in it for the scares and is nice enough to do it while you're already on a toilet, sparing you a change of pants.
Unfortunately, there is no way to avoid him unless you never use a bathroom again but that might be difficult. He is just a nuisance that you may have to put up with but at least he isn't actively trying to kill you like most of the creatures in this guide.
*It's been reported that he will sometimes wear the face of a loved one before revealing his true form
FUN FACT: People often