Why?

It's like a mother marrying her child, they hate the husband :D and probably because they don't want him to be eaten by a big bad wolf. But why is Nanao ( Mikado's older bro) is hated you'll need to read his story, he's notorious gay and there are rumors surrounding him in college where Kuon also attends and he told his brother about it too.

Yeah but aren't they both gay (or bi)...? I don't see hey they hate Nanao...

In this story it was before Nanao succeeded in making Kuon fall for him, so far both of the brothers are straight and find their little naive brother is being manipulated by an evil cunning person, since Towa is the youngest and most loved brother they're on Guard and hating on Mikado and his family ( the loose perverted brother )
Later on, Kuon will love Nanao but still refuses Mikado. Also the eldest brother will like Nanao but still hating on Mikado

Oh! I think I'm confused because I read Mikado's and Kuon's story first Σ( ￣□￣||) thank you!

You poor soul! Let me enlighten you a bit ε=ε=(ノ≧∇≦)ノ

List of Warui Series:
Vol 1 Warui Koto Shitai [1-1]
Vol 2 Waruiko Demo Ii? [1-2]
Vol 3 Kirai ja nai Kedo [2-1]
Vol 4 Koi Ja nai Kedo [2-2]---
Warui Koto Bakkashite Gomennasai [1-3 & 2-3]
Vol 5 Warui Yatsu Demo Ii [1-4]
Vol 6 Mujihi na Otoko [3-1]
Vol 7 Warui Koibito ja Dame? [1-5]
Vol 8 Kare ja nai kedo [2-4]---
Warui ko Tachi no Bansan [1-6 & 2-5]
Vol 9 Mujihi na Anata [3-2]
Vol 10 Sunao ja nai Kedo [2-6]
Vol 11 Warui Ouji Demo Suki [1-7]
Vol 12 Mujihi na Karada [3-3]
Vol 13 Shouwaru Ookami ga Koi wo Shita Rashii [4-1]
Vol 14 Himitsu ja na [2-7]

1: Towa and Mikado
2: Shinonome and Yuki
3: Nanao and Kuon
4: Akagi and Nao

You better put another Pair below Akagi and Nao, which is Nao's brother Hayate.

are you a god? if not then now you are