I'm confused about the good ending (spoilers).

[Bug Enthusiast]

So I get that the grandpa was just there to manipulate you into feeding them until he (the predator) could take care of itself, but what I don't understand is why it decided to actually help you (the girl) with your (her) parents. If it could fend for itself, why didn't it just leave? Its not like the girl could have stopped it. Does anyone have any ideas as to why this must be? I and a friend are really stuck on the thought.

[Jorkey!]

Through many of the documents you can find information about magic and demonic activity. For what I understand, Whiskers (the hairy thing that takes the form of Grandpa) is the "Angel of Needles" mentioned in the magic book you pick up at the very beginning. Whiskers is a demon-ish creature that can look into people's minds and shape itself to its grower's wish in order to better comunicate with them. Whiskers is looking to propagate, and apparently it can only do so by possesing a human body, when Adrienne came into the basement and freed it, by making a wish she made a contract with Whiskers.
After week 4, if Adrienne has not fulfilled her part of the deal (handing to Grandpa the paperdolls and a blood offering. Note how in the magic book it is specified that the researchers are not allowed to make gift or offerings to the "sample") the demon would not fulfill its part either and passes to posses Adrienne (you can read about how demonic contracts work in the book that's in the bookshelf on the dark corner), but in the good ending, Adrienne does complete the ritual and so Whiskers possesses her parents to make her wish come true.

At least that's what I got from the story, though there are some things I might be missing!

[Red_Rosa]

I might be wrong but I think to understand why Grandpa fufills the wish you need to view the story less literally and look more at the metanarrative it's trying to tell. I haven't fully comprehended it but I think Grandpa, Adrienne, and her parents are supposed to be representative of the cycle of how childhood trauma and neglect produces traumatic and neglectful parents who then continue to reproduce the cycle. The good ending (I understand it to be good at least if not literally in the world that it takes place in) where you get the wish is the by product of Adrienne breaking the cycle. Grandpa whilst being her grandpa is definitely coded to be child like (you feed them, you teach them, their identity is defined by their peers/creator). To get the good ending you have to give it your own blood and feed it meat both of which require some sacrifice or caring on your part. In the story there is also potential that Adrienne's real grandpa was demeaning to her mother (as shown by when he threw away the picture of her boyfriend and joked at their expense presumably) which further emphasises how far up the cycle has gone than just between her and her parents. Grandpa simultaneously being Adrienne's grandparent and her own child to care for further hints at the cyclical nature being both before and after her. I don't know though, my interpretation is probably off.

[Freylaverse]

Originally posted by Red_Rosa:

I think to understand why Grandpa fufills the wish you need to view the story less literally and look more at the metanarrative it's trying to tell

I think looking at the metanarrative does make it more clear. However, if you want a more literal explanation, I have one that I think is somewhat plausible!

I don't think Whiskers fully understands what it's doing with the things Grandpa says, but I think it knows what Grandpa ought to say and do. A bit like how ChatGPT probably doesn't "understand" its words and their implications the way we do, but it can still hold a conversation based on what it knows about how people usually respond to certain combinations of words. And at the end of the game, Whiskers is in equal parts acting like itself - the creature - and like Grandpa, or rather, Whiskers' interpretation of Adrienne's idea of what Grandpa should be like. I'm sure Whiskers doesn't really care about Adrienne or her parents, but it knows Grandpa ought to. So, before Grandpa is cast off as no longer needed, he still gets some say in what they say and do. And Grandpa had decided to uphold his end of the bargain.

Alternatively, if you want the more mystical explanation, Whiskers is some kind of supernatural entity bound by its contracts the way a genie is. That's the easier one imo, but it's less fun.