*The series alternates between different sets of pairs. Although it’s supposed to be read as a whole, you can skip volumes with the pair(s) you don’t like.
Warui _____
Featuring the school delinquent Towa Aikawa and the student council president Mikado Shirahane. (Pair 1)
V. involving this pairing are: V.01, V.02, V.04, V.07, V.11
_____ ja Nai Kedo
Featuring Shuuji Yukimura, the formidable student council vice-president, and the problematic childhood friend, Ryuuichi Shinonome (Towa’s friend). (Pair 2)
V. involving this pairing are: V.03, V.05, V.08, V.10, V.?
Mujihi na _____
Featuring Nanao Shirahane (Mikado’s older brother), a male siren, and Kuon Aikawa (Towa’s older brother), a fellow student attending the same university. (Pair 3)
V. involving this pairing are: V.06, V.09, V.12
Shouwaru Ookami ga Koi o Shita Rashii (Wicked Wolf Seems to Be in Love)
Featuring former student council president, Shirou Akagi (Mikado’s rival in Warui Koibito and Warui Oujii) and disciplinary committee member, Nao Kousaka (Yukimura’s rival in Sunao ja Nai Kedo). How will those two damaged people find their respective love? (Pair 4)
V. involving this pairing are: V.13
Special chapters:

Title(s) in colors are still being scanlated.
Reading Order (taken from the official website): (Volume number - Title [Pair number - Appearance number])
v01 - Warui Koto Shitai [1-1]
v02 - Warui ko Demo Ii? [1-2]
---- Suki Sugite Gomen ne
v03 - Kirai ja nai Kedo [2-1]
v04 - Warui Otoko Demo Ii? [1-4]
---- Warui Koto Bakkashite Gomennasai [1-3 & 2-3]
---- Neko todo S Nadeshu Nyuu-sama
v05 - Koi Ja nai Kedo [2-2]
v06 - Mujihi na Otoko [3-1]
v07 - Warui Koibito ja Dame? [1-5]
---- Osawari de Enryo Negai Masu
v08 - Kare ja nai kedo [2-4]
---- Warui ko Tachi no Bansan [1-6 & 2-5]
v09 - Mujihi na Anata [3-2]
v10 - Sunao ja nai Kedo [2-6]
v11 - Warui Ouji Demo Suki [1-7]
v12 - Mujihi na Karada [3-3]
---- Kira-senpai to Kokonoe-kun Gekokujou [4-0]
---- Non-Fiction
v13 - Shouwaru Ookami ga Koi o Shita Rashii [4-1]
v? - Aikawa Ka no Konton Taru Mirai [5-1]
v? - Himitsu ja nai Kedo [2-7]
*Only extra not scanlated.
*On-going.