Afanc, also known as Addanc, is lake monster from Welsh mythology. It can also be traced to British and Celtic folklore. Sometimes described as taking the form of a crocodile, giant beaver or dwarf, it is also said to be a demonic creature. The Addanc was said to attack and devour anyone who entered its waters.
According to one tale, it was rendered helpless by a maiden who let it sleep on her lap; while it slept, the maiden's fellow villagers bound the creature in chains. The Addanc awoke and, enraged, killed the maiden. It was either dragged away to lake Cwm Ffynnon, or killed by Peredur.
In the tale, Peredur son of Efrawg, the "Addanc of the Lake" resides in a cave near the "Palace of the Sons of the King of the Tortures" — so named because the Addanc slays the king's three chieftain sons everyday, only for them to be resurrected by the court maidens. Peredur ventures to the cave on his own, wishing to kill the creature to increase his fame and honor. On his journey, he meets a maiden who says that the Addanc will slay Peredur through cunning, as the beast is invisible and kills his victims with poison darts. The maiden, who is actually the Queen of Constantinople, gives Peredur an adder stone to make the Addanc visible. With the aid of the stone, Peredur pierces the Addanc and beheads it.
"A giant monster that looks like a giant beaver, it dwells in the Conwy river which is located in the north of Wales. It creates whirlpools and drags down those who look into them. In addition to that, the Afanc is physically stronger than a group of adults. However, its weakness is maidens. By using one as bait, it is possible to capture an Afanc."
Devil Survivor 2
"A lake monster that looks like a giant beaver, said to dwell in stagnant rivers. It causes whirlpools and drags down those who look into them. Its strength is monstrous, greater than many men together, but it is weak in the face of a maiden. There is a tale where one was lured onto land and ended up captured by the powers of a bull."