Description
Kekkai are a kind of sankai—childbirth monster. Details are sketchy some say it's like a turtle some say a monkey.
When a kekkai emerges, covered in blood and amniotic fluid, it quickly scampers away from its mother and tries to escape. This is most often accomplished through the irori, or earthen hearth, a common feature in old country houses. It either burrows down beneath the floorboards, or climbs up the long pothook which hangs above the irori and flees. If the kekkai is able to escape, it will return later to kill its mother while she's sleeping. It does this by burrowing up through the floorboards and into its sleeping mother, tearing her apart.
The opening in the floorboards being like a child birth was done on purpose since its a nightmare fuel demon.