The brainwashing wouldn't actually work if they didn't feel anything negative toward emi, the shopkeeper said that when remuria had him by the neck. So basically they have something against emi from the start and the potion just triggers them to act on it.
If you read the novel, you will see why they all deserved it, especially the fiance. I highly recommend it - you can see their pov on the side stories
Do you have any where to read it at ?
Oh if that's the case then that's a different matter. I hope you're right then I won't feel guilty when they suffer anymore
Don't get me wrong, those boys deserve it but I do not feel ENTIRELY good when they are suffering because I know for a fact that they are being brainwashed. Hays, I just have soft heart when it comes to revenge like for example, I see the villains suffering, I can't see them die or being tortured unless they are truly bad to the core and just too evil.