The Abumi-guchi is a type of fur-covered tsukumogami (a creature that was once an inanimate object, usually a tool) that is formed from the stirrup of a mounted soldier who was killed in battle.
In the Gazu Hyakki Tsurezure Bukuro (The Tedious Bag of One Hudred Vessels), a book published by illustrator Toriyama Sekien in 1784, a drawing of the Abumi-guchi is accompanied by the following poem:
An arrow is shot deep into the knee, he falls from his stirrups, the hand of suffering is dealt, and such a song is sung, I saw it not in my dreaming mind.
This obakemono is the least interesting monster for me, mainly because Toriyama's original design is pretty uninspired; it looked more like one of those "Yip Yip" martians from Sesame Street with a stirrup for a mouth and ropes for arms. So I redesigned the creature to look more like a squid (a la Hokusai's "The Dream of the Fisherman's Wife") with the stirrup on its head like the mouth of an Angler fish.