My favorites.

Spin-off about Gorou and Verde here : http://www.mangago.me/read-manga/kimi_to_kore_kara/

Spin off about Rei and Shougo here : http://www.mangago.me/read-manga/back_stage/

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]
Vol 9 Mujihi na Anata [3-2]
Vol 10 Sunao ja nai Kedo [2-5]
Vol 11 Mujihi na Karada [3-3]