I think this will help (me and other readers) to understand the whole thing and it's correct order @~@ this section is good to help us remember d^-^b
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.05, V.07, V.12
_____ 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.04, V.08, V.10
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.11
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
Reading Order:
Volume number - Title [Pair number - Appearance number]
V.01 - Warui Koto Shitai (I Want To Be Naughty!) [1-1]
V.02 - Warui ko Demo Ii? (I'm a Bad Kid, But That's Okay, Isn't It?) [1-2]
V.03 - Kirai ja nai Kedo (I Don?t Dislike You) [2-1]
V.04 - Koi Ja nai Kedo (It's Not Love) [2-2]
---- Warui Koto Bakkashite Gomennasai [1-3 & 2-3]
V.05 - Warui Otoko Demo Ii (Is Even a Bad Boy Good?) [1-4]
V.06 - Mujihi na Otoko (Merciless Man) [3-1]
V.07 - Warui Koibito ja Dame? (Can a Bad Boy Be a Lover?) [1-5]
V.08 - Kare ja nai kedo (I'm Not Your Boyfriend) [2-4]
---- Warui ko Tachi no Bansan [1-6 & 2-5]
V.09 - Mujihi na Anata (Merciless Lover) [3-2]
V.10 - Sunao ja nai Kedo (I'm Not Honest) [2-6]
V.11 - Mujihi na Karada (Ruthless Body) [3-3]
V.12 - Warui Ouji Demo Suki (I Love a Prince Even If He Is Naughty) [1-7]
---- Kira-senpai to Kokonoe-kun ~Gekokujou~ [4-0]
V.13 - Shouwaru Ookami ga Koi o Shita Rashii (Wicked Wolf Seems to Be in Love) [4-1]
I Want To Be Naughty!