OK, so I've seen the entire series
plus the OVA. But what struck me, particularly with the events in the OVA, was that perhaps Hazumu did not choose Yasuna really out of "love" per se, but out of "pity"? I mean, even Yasuna admitted her selfishness because of her condition, that she had to rely too much on Hazumu, who in turn was too kind to leave a helpless Yasuna on her own and go to the one who truly understands her (Tomari). Which is what exactly happened!
And weren't they setting this up even in Episode 12 as they ended with Yasuna and Hazumu saying..."You know..." ?