Yomi no Tsugai - Vol. 2 Ch. 8 - Sincerity and Murderous Intent

[MangaDex]

 

[PhantomJoker9]

So basically Tsugai are Jinn and these are all Devil Worshippers who made contracts
Story seems to be supporting Japanese view of Satanism which is odd
But looking at all the human sacrifice in Fullmetal Alchemist it starts to become clear