pairing 1 - Towa x Mikado
pairing 2 - Kuon (Towas brother) x Nanao (Mikados brother)
(pairing 1+2 are entangled, together they go about 10 parts)
pairing 3 - Yukimura x Shinonome (best friends of Towa and Mikado)
pairing 4:
Kousaka (disciplinary commitee member) x Akagi (ex student council president)
pairing 1 - Towa x Mikado
pairing 2 - Kuon (Towas brother) x Nanao (Mikados brother)
(pairing 1+2 are entangled, together they go about 10 parts)
pairing 3 - Yukimura x Shinonome (best friends of Towa and Mikado)
pairing 4:
Kousaka (disciplinary commitee member) x Akagi (ex student council president)
= couples who are blood-related or know each other somehow otherwise
additional are the series in the following lists:
http://www.mangago.com/home/mangalist/6968/
http://www.mangago.com/home/mangalist/7543/
http://www.mangago.me/home/mangalist/8347/?filter=&page=2 (just the Kuroneko series)