Holy shit, this Christmas update fucking sucks. It's obvious that this was rushed, as the visuals definitely aren't up to par compared to the other updates. I mean everyone just looks so much more rough, and the posing is pretty shoddy in several places. I mean I imagine the dev had to make/use all new models for this update, which again feels insane for such a waste of time and effort.
Not only that, but it seems like they're making this flashback canon, which just totally destroys the attempted world-building (which was already shaky anyway). How "The women in your family have Christmas magic, Santa fucked your mum and you're his kid, your 'protector' fucked your sister, and your magic demon powers came from Santa" is supposed to make anything stronger is just...insane to me.
Also, technically speaking, by the new planned tags list this may also technically constitute as NTR, even if it isn't shown ("netorare: A love interest has sexual contact with someone else without the approval of the protagonist"), although I think using the older definitions it should still be fine.