I'll start by prefacing (again) that I have no direct involvement with this AVN, meaning what I know is what I gathered from the synopsis in the OP, and by playing what's currently available, so mine are just "devil's advocate" speculations.
This is how the FMC is described to us
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I read that and IF I ignore we are playing an AVN what I expect out of this character is not to be sexy, but to be tough,
which would make sense after 6 years of living in a post-apocaliptic scenario , what I expect instead from the original partner of our MMC is to generate in us emotions
once we (as the MC) are faced with reality of losing her, just couple of weeks into the whole mess , I think so far they both achieved the goal.
Then of course this is an AVN so if folks don't find a character attractive it can be an issue, but she's not a LI, she's the protagonist (together with the male MC), no idea how the story and interactions will develop, how many times thou have we played AVNs where the MC is really not that great/good looking, but we still ended up liking the actual LIs?