First this is comment number 69, Kaela would be proud. And is it bad that the first thing that came to mind when the parents told them the truth was another manga:
https://mangadex.org/title/d3221e7b...5fb03c/my-sister-who-cannot-stand-me-is-scary
Check it out if you get the chance, there is also an NSFW version of it around if you want that one instead. But beyond that, this premise is interesting. Normally these types of stories don’t get serialized and are instead relegated to doujin circles, so this is a nice surprise. Hopefully this winds up being good, and that the characters are better fleshed out in the future. For a first chapter this is pretty good with a nice set up, but I probably would have held off on jumping into the talk they had until the next chapter at least, let us see how the two of them are as is for a day, and then at the end start the talk leading into the next chapter. That way we have a nice prelude, and we familiarize ourself with the characters and setting first before it changes dramatically. Otherwise the shift won’t have as much of an impact as it otherwise could, as it is it’s fine, not bad, but could definitely be better.
It would have been nice if we got to see how certain things were between them before the talk, and then how they changed immediately following it. From how she dresses in the morning, the cups she drinks from, the way she talks and treats him in general, etc you get the picture. A nice before and after kinda deal y’know? That manga I was talking about before does that, but it’s in every chapter as a before and after type of thing, instead of it being the first one only.