My theory is that the Oni Masks were created by those warlords Hutchins mentioned in S8. They are called Vengance, Decepition and Hatred. The main warlord is Vengance who has four arms. Hatred has indestruciible armor and Deciption is just a simple Oni but he can levitate things. But the real leader is the first Oni (If you have name ideas write them) who is the father of all Onis including the 3 warlords. Since the Mask of Vengance is the only Oni Mask existing they will likely try to find it. If you have any theories about the Oni this is the right place to put them.