At first I wanted to comment on how this, indeed, isn't funny for shit, and is more akin to psychological horror.
But now, I want to point out the sheer amount of broken engrish comments who write shit like
Nah fr how tf this shit got the devils number and at most its like a mid 7 ish😂
Yeah....the sister is a crazy ahhh bi*** 😭✌️
And to reply to something else:
I don't get the low rating, this is pretty aight. I'm bookmarking.
I mean, really?
This is a manga that seemingly "baits" the idea that this is a chill romcom, but incredibly quickly reveals a yandere-type plot where the sister is immensely possessive, and is one short step away from raping her brother and ripping his head off. This work seems to aim to unsettle the audience, more so than to build any genuine relationships, or throw jabs or jokes.
There's nothing practically wrong with that sort of a story, in theory, but pulling a "madoka" like that rubs people the wrong way, especially if it pops on the front page.