Well... She is supposed to be Evil, so it makes sense, in a corrupted way. If something, the Hero and his fetish are to blame for this fucked up situation. Time for him to be turned into a tool against the Demon Lord.
With so many actors wanting Iruma for their own purposes... I say a civil war is the least violent of the outcomes.
Plus, even if Iruma is finally deported... that doesn't mean he cannot return to the demon realm through similar methods.
"Sakisa"? With that long, dark hair and longsword (probably, a zweihänder), I think it might be Delta in disguise. While I do not think she has enough intelligence/patience to play such a role very well... her appearance, weapon of choice and original name (Sara) match just enough to make me...
It seems they ended up in the Bloodborne level... with the associated spike in difficulty.
Rest in peace. Your friendship really was a light in the dark.
Edit: It is OK to be angry. I am too. I am just coping in my own way.