I feel like Calli should be weighing in on this, as my next-door neighbor. If she's got a demon baby, she's doing an excellent job of disguising it as a friendly cat.
Leifur is lulling us into a false sense of adoration. If I attempted to put a diaper on him—with a hole cut out for the tail or not—I'm sure his demonic nature would emerge.
Maybe that's why C never has anyone over!
Demon sister there, not a demon baby.