Interestingly enough, Mio has so far had a positive impact on Doubara's life, but it's pretty easy to see it's only the first impact. He technically does see her madness, which is why he has tried to make sure she doesn't take any shortcuts (suicide), but I reckon he doesn't really understand its depth. The more he starts to like her, the harder it will be for him as well, to worry 24/7 that she will kill herself. Furthermore, before long it might start to bother Doubara that nothing else really matters to Mio anymore, even if she does still function as a person.