Akaname is a yokai that appears from human filth and scum. On the left you can see him as depicted by the Edo Era artist Utagawa Yoshikazu (歌川芳員). Some explanations say he is actually born out of the scum. At night while everyone is sleeping, Akaname comes and licks the filth from the bathroom and old unkempt houses. Due to his name and attributes, he is usually depicted with a long tongue. Because the word “aka” also means red (with different kanji), he is often depicted with a red face or body.
According to some accounts, Akaname also licks the filth from sleeping sick people. I read on a blog that he also licks the filth from people who hate baths, but that’s not really substantiated anywhere else I looked. Some people associate Akaname with kami since he doesn’t really do anything bad (how bad is it to have a weirdo come clean your bathroom for you?). And in the children’s book I own called Yokai no Daijoushiki (Poplar publishing, 2004), it says nowadays we don’t see Akaname anymore because bathrooms are made of tile and plastic, not wood.
In Edo times, it’s likely the bathroom was hard to keep free of mold, scum build-up, and wood rot. The Akaname served as a reminder to clean up as best one could. The Japanese Wikipedia page even postulates that since the word “aka 垢” also referred to evil desires in one’s mind, the story of Akaname tells us to keep evil thoughts from building in our minds or we may be transformed into filth licking yokai. Deep, eh?