Ittan-momen is an effect NPC that resembles a fluttering beige towel with two dark red eyes. It can be found in the Infinite Wilderness to the left of the Hot Spring House. The Towel effect can be obtained by interacting with it.
The name Ittan-Momen comes from the Yokai with the same name. An Ittan-Momen is a Tsukumogami (an object which became 100 years old and came to life) and looks like a "long, narrow sheet of cloth normally used to make clothes". They fly around at night and attack people by wrapping themselves around the head of the victim and strangle or smother them to death.