This spin-off of Reimu comes from the Japanese slang for fat, debu. Although opinions differ on what exactly constitutes a deibu, there are some oft-used characteristics:
fat and/or ugly (usually due to overeating, may appear bean-shaped)
very arrogant and selfish
violent and quick to anger
very protective of her children, to the detriment of everyone else; unable to see children's faults (but in a desperate situation or if she is angered, will quickly abandon or even kill her children to save herself)
generally only cares for the reimu-type children; (which is actually a common trait for most reimu-types) children of her mate's type are often either neglected or outright killed
demands favors and candy from humans
kills off good yukkuris
claims of being a pitiful single mother (Deibu-only trait)
is usually is the one who causes her mate to die in the first place (often by not sharing any food with said mate)
usually gives birth to equally unpleasant children like herself.
Most of the time (but not always) deibus get what is coming to them.
The pioneers of modern-day deibu are gesuaki and z-aki; check their works if you want to know precisely what a deibu is, as just about every yukkuri they draw is a deibu or the respective equivalent of a deibu aka bawiza, awize or batchouli.
