Evil hero, huh? Could Flay's father possibly be a former party member of said hero? And hero kicked him out for being "incompetent" but was actually op? Maybe not.
I had a weird feeling that Naru might still be alive considering we never saw anything to do with any of the bodies from the orphanage after the fire just that Flay thinks she is dead along with everyone else (which who knows maybe none of them are actually dead).
Edit: nevermind...went back to chapter 2 and it makes so much more sense now. I fully subscribe to this theory without much question. Also, I totally forgot one simple line from chapter 2 and didn't make the connection.
Well, Rose seem to really like the MC. But why? She must knows him before all this. And maybe the reason she cannot smile is because she is an undead or something similar.
Naru told him that he would a good teacher.
In ch.2 Rose said that she knew he would be a good teacher.