AliKari is always good for the heart...
Until you remember Alina is an unstable psychopath.
I don't think this is fair, Alina's behavior is always starkingly different around Karin, and while she is harsh towards her she has never shown a hint of hostility towards Karin, the first Halloween event even shows that Alina is willing to put herself in a vulnerable position and do things she admits she is terrible at if it is for Karin's sake.
That's the beauty of their relationship, for all their insanity, Karin grounds Alina, and Alina is able relax around Karin.