Alright so I gave this a try because of the proportions, the sisters also pretty hot but I would not dream of expecting much of this letting alone supporting it in it's current state.
The game has no music, never a good sign.
You notice a failure to have a capital at the beginning of sentences within some of the very few starting lines.
I know it's the first update but the purpose of a first update is to make you care, why do new devs expect to be supported when they fail to show they can deliver, blueballing only works for masterful story tellers.
It looks to be split 50/50 choosing between incest and NTR, so that means half content for a lot of people, in fact some of "vanilla" content was a dream about the sister laughing at the MC's tiny dick, I mean I know people are into that but again most aren't.
I don't consider anywhere near NTR but I find it funny that in the non-ntr route a guy falling unconscious on top of your sisters chest got further than the MC
I actually have a high tolerance for stupid MC's but the MC is not simply stupid, he doesn't act like a real person, no one see's their topless sister hiding in an alley and screams out "are you a whore, where you graped" I am not sure if graped was intentional or not.
The dev should also be aware patreon doesn't like step siblings.
You had the sister stop 2 separate attacks in the first update, better prioritize what to focus on.
Also it's another one of those games that's set in Japan but there was like one background asian.
If the dev didn't use an AI to write this then work at their writing, write the protagonist more like a real person, spend a bit more time on their relationship and the curse, maybe make it a family curse, say the curse feeds on taboo and why she's horny for bro, add the mom, people love moms. If you're going to stick to Japan say they have a Japanese grandmother or something and background characters should almost always be Japanese.
Now as for the NTR, seems like the 50/50 thing is going to be a mess unless you break your balls working at this.