I guess heroes and "witches" are the same thing based on what we just saw.
So, this is the first serious trouble for the MC in this story. The demon king arc enemies were somewhat tough and tricky to fight against, but I don't remember them being a direct, existential threat like this. Not even guns and seemingly OP heroes kept him safe, in fact Atou's power was literally used against him...
Now I'm keenly interested in what's going to happen next. Their current strategy of quiet development to avoid war clearly stopped working with this, and an (attempted...?) assassination of a country's leader is an obvious casus belli. I'd be surprised if war doesn't result from this event.