They’re pretty self-explanatory: Slime girls are girls made of slime. They’re partially transparent, so you can see everything that’s, uh, inside of them. Depending on the fandom and/or canon you ascribe to, they can envelope other people and objects, and their legs sometimes puddle on the floor.

Welcome to Rule 34, a series in which Motherboard’s Samantha Cole lovingly explores the highly specific fetishes that can be found on the web.

“Slime girls used to be a lot more niche, but the popularity of the Monster Girl Encyclopedia , [the erotic game] Monster Girl Quest and later on the anime Monster Musume have definitely lead to an explosion of new content,” Celladoore said. “My first exposure to a slime girl was from an episode of Sailor Moon that aired in 1995, so I would guess the trope began somewhere between the late 80s and then.”

Slime and goo girls might seem like something born out of spending too much time on DeviantArt, but they’ve existed at least since the 1970’s, with the Oozes of Dungeons and Dragons . From there, they’ve trickled into other, more modern role-playing video games and manga.

I asked u/Celladoore, one of the mods for the Slime Girls subreddit, how she ended up modding such a unique, sticky corner of Reddit. “I've always liked monsters and monster girls ever since I was a kid playing role-playing games and reading about them in mythology,” she said. “I find monster girls strange and fascinating, and as a woman, I've always liked the idea of how powerful and unrestrained they are. For slime girls, in particular, I love how dynamic they are, and the play of light and color is beautiful to me.”

Someone on the r/slimegirls subreddit titled their image “a girl who is also lube." That really nails it, so let’s start start there: The sub is currently 17,000 subscribers strong, and devoted to posting illustrations and musings about their favorite gooey girls—not always in a NSFW way.

Two kinds of slime girl-like creatures that appear in the Sailor Moon series include Peropero , a shape-shifting demon minion that’s a mass of green gel sometimes in the form of a bunny, sometimes a woman, and Jamanen (Jellax in the English dub), a “nude, near featureless lady with a red coloration and supple body.”

Urban Dictionary, the only place I could find a Latin-named definition of this fetish, calls it “limophilia,” as “limo” means “slime” in Latin, and “philia” is “love.” I couldn’t find limophilia referenced in the context of slime girls anywhere else, however, so this is probably made up by a user contributor. Still, it sounds professional so let’s go with it.

A good many goo girl creations are based on a character named Suu, from the manga Monster Musume: Everyday Life With Monster Girls. She’s a Slime, which the Monster Musume fandom defines as a rare, “liminal race whose bodies are composed almost entirely of a gelatinous substance.”

There’s definitely a touch of fem-domme fetish in some of these creations, an assessment Celladoore agrees with: Monster girls, in general, have a dominatrix quality, with sexual partners as their prey.

“Many people like the idea of restrained/smothered or in some cases even absorbed,” she said. “Some people with transformation fetishes like them, and enjoy the idea of being turned into a slime girl.”

According to the Monster Musume canon, Slimes eat using phagocytosis (a term borrowed from cell biology, meaning they envelop their food to absorb and consume it) and reproduce through "splitting and fusing,” a process I’m incapable of paring down in conscience terms so please just read the whole description:

“At a certain point in its life cycle, a slime will split a part of its mass to form a new slime. This new slime will then embark on its own to gain nutrient and experience until at such a point that it has gained enough nutrient and/or experience to become desirable enough to be absorbed by another slime or it finds a slime that it may desire to absorb. At this point, the new slime will absorb (or be absorbed by) the other slime and the pair's combined experiences and nutritional makeup will form a completely new slime that is ideally superior to their previous individual forms. This newly formed slime will then embark to live its life until eventually opting to split parts of its mass to form more new slimes which will embark on their own to gain nutrient and experience, thusly repeating the cycle. It is assumed that this cycle of "splitting and fusing" repeats several times throughout a slime's lifetime.”

All of this might be starting to sound intimidating—the cell biology, the DnD, the manga—but at the end of the day, it’s very simple and tactile.

“The most obvious attributes are simply they are extra soft and squishy, usually transparent so you can see everything going on inside of them,” Celladoore said. “And of course, there are no defined entrances, so anything goes.

Top image by Nanoless on Patreon