Charybdis

Charybdis are an aquatic subspecies of Mimic, that live on the seafloor inside a giant barnacle. They snare men by sucking them underwater with giant whirlpools. These monster girls have many extra holes in their exoskeletons, and are implied to be fans of gangbangs; a baphomet of the Sabbath remarks in Monster Girl Encyclopedia I that charybdis are big fans of doppelganger medicine. Their natural enemy is the scylla, who keep sneaking into charybdis' lairs to try and snare humans that the barnacles have sucked underwater.

Encyclopedia Entry
The Charybdis is a monster that lives fixed to the bottom of the sea in a nesting hole like an acorn barnacle. They don’t turn into something and set a trap, but due to their nature, they are classified as a kind of Mimic. It is said that there is another dimension conjured from magic that extends inside their nesting holes in the same way as other Mimics. Condensed demonic energy is contained within their bodies, so they occasionally release it through holes in their exoskeletons. Due to this, air bubbles often rise from their nesting holes.

In order to get a human man for food and breeding, they periodically generate huge whirlpools focused around their nesting holes. Everything above their hole gets sucked inside. Although they are timid, they are extremely lustful, and when they suck a man into their nesting holes, they spread their vagina open with their own fingers and tempt the man. From their open vagina, they release so much condensed demonic energy that it makes the energy released from the holes in their exoskeleton seem like nothing. The man is showered in it, and in moments his stiff penis will likely be thrust inside her vagina as if it had been sucked in.

Charybdis are extremely greedy, so once they have a penis in their body, they entwine their arms and legs around the man, binding him. They covetously suck the penis in order to gain more pleasure, trying to guide it deeper and deeper inside. Also, the holes in their exoskeletons have walls that are very sensitive to pleasure. Though it is slight, from these holes, and even from the open mouth from which they speak, they release demonic energy to seduce men. Men are attracted by it. It’s probably that way so they can indulge in many pleasures, sucking a penis from every one of their holes.

Through the whirlpools they often swallow up whole ships, including all the sailors, but all men except those who strike their fancy are spat out of the nesting hole. Some of the men spat out find themselves washed ashore on the beach when they regain consciousness, but most of them are captured by monsters lurking near Charybdis. When they come to, they find themselves in the middle of having sex with them.

Due to these opportunities, there are normally a lot of Scylla in particular that lurk around Charybdis nesting holes to aim for the men that are spat out. Many of the tales told involving Charybdis also involve Scylla.

Being timid themselves, they can’t say it strongly, but because Scylla often drag off all the men while the ships are stopped by the whirlpools, it seems Charybdis don’t think very highly of the Scylla.

Trivia

 * This Monster is based upon the Ancient Greek sea monster Charybdis. Charybdis swallowed up entire ships and their crew by creating giant whirlpools. Nearby was the monster Scylla and sailors passing through the area had to choose between facing (and surviving) either of the two, ergo the idiom "Between Scylla and Charybdis".