Now I know what to call that tree Dev wears as a hat!
I officially declare its name to be Blood Tree! *smashes a bottle of champaigne on the trunk*

And there's a bit of a background story for how the Devourer originally got the tree into his possession.
The Blood Tree resided on a graveyard, seeping nutrients from the rotting corpses (see eyeflowers as well!), but for some reason Devourer could understand its wish to go and find fresher nutrition for its roots to find. At first the Devourer didn't bother to help the tree but then he learned that it could offer him so much more in return. It started a symbiotic relationship for the two.
When he placed it on his head, it rapidly sunk its roots deep beneath his hair and into his head - but it didn't harm him.
Thus his veins and the tree's roots were connected, only until he took the tree off for a while.

As a parasite on his head, the tree stole part of the nutrition Devourer got from his meals - human flesh. But it would pay off later, as when the Blood Tree blooms, the flowers are dyed red and it emits a soft but enticing aroma which lures people near Devourer. It's hard to tell what the aroma consists of - pheromones, soul particles - but it attracts people like flies.

In the Devourer's eyes, humans are children of light, no matter how dark deeds they have done, they always have an aura of light about them, were it dim or very bright. And he always finds satisfaction in killing the light.
The theory of light applies to the Sun People in its most literal form. They are always warm and caring about their kind. But now the blood blossoms have made them nuts - the air is so full of love that they don't notice the cold beast that eats them up one by one. (with the dimming light inside his belly)