Yeah, who would have though the series called "My Little Sister Can't Be This Cute" that was filled with incestuous undertones would end with the MC hooking up with his sister.
Also, still doesn't excuse death threats.
Oh I'm not excusing those, believe me. I'm more just saying those that say the ending (or the second season or the whole series, really) was an abomination aren't saying it because of shipping reasons (well, that probably does factor in a bit, to be fair), but because of the exact nature of the ending. Death threats are a bit...extreme, though.
(I wasn't surprised by it, either. I mean, yeah, its in the damn title and filled with that stuff)
That's a real thing that happened, huh? WOW.
It gets weirder, really.
From what I recall (I never watched the show, I couldn't stand it. I only saw the aftermath), the author had pressure put on him by editors/higher ups to not have the MC end up with his sister. The author then has the MC break up/shoot down each and every one of the other girls who like him and goes through with a faux-wedding with his sister, only to break up a few months later since they realize the nature of their relationship can't work out.
So basically, the author torched every single ship pairing for the sister and then even kinda destroyed that one. No one was happy.