Calling it an allergy is weird though... I think it's closer to aversion to a certain type of interaction, which is 'kindness' in this case.
Well, if someone who had always acted like I'm an eyesore suddenly turn a 180 and be kind towards me, I guess I'd feel nauseous, too.
I'll pretend Mizu was either born a sociopath or simply developed into one without torturing animals, going on any murder sprees or offing her mother.
Does not help much but at least it makes her personality at least a bit more believable.
Still, there is SOME truth behind the "allergy to kindness" farce - some people tend to get weirded out or even turn hostile when presented with behaviours that set them off the wrong way... but to call this an "allergy" is just stupid.