So from that conversation with Eric I think he wants rei more than sauro however if what he says is true he will be disappointed no matter what not all the people is gonna be bad and not all is gonna be good Arsenio needs to be realistic without falling in depression on the other hand from what I've seen so far the obvious option would be rei but it also depends on how much chapter are left and if the author wants to add a plot twist
The Witch's Servant and The Demon Lords Horns