Any good hardcore BDSM suggestions? Doesn't necessarily have to be yaoi...
Blood bank
http://www.mangago.zone/read-manga/blood_bank/
http://www.mangago.zone/read-manga/mud/ not really hardcore but it is amazing
http://www.mangago.zone/read-manga/yoru_wa_tomodachi/
http://www.mangago.zone/read-manga/partners/
http://www.mangago.zone/read-manga/hoshi_no_yakata/
http://www.mangago.zone/read-manga/motto_musunde_aite_waya/
http://www.mangago.zone/read-manga/midnight_dog_show/
http://www.mangago.zone/read-manga/ronald_no_yabou/
http://www.mangago.zone/read-manga/konoyo_no_hate_made_i_love_you/
this ones kinda fit->
http://www.mangago.zone/read-manga/venus_ni_seppun/
http://www.mangago.zone/read-manga/tokushu_ninmu/
http://www.mangago.zone/read-manga/henai_fumouhen/
http://www.mangago.zone/read-manga/gintama_dj_ride_on/
http://www.mangago.zone/read-manga/gintama_dj_akarui_kankin_seikatsu/
http://www.mangago.zone/read-manga/hentai_play/
Pretty much anything by Zaria Ranmaru has elements of it, but Void and Pet Keiyaku in particular.
http://www.mangago.zone/read-manga/void_zariya_ranmaru/
http://www.mangago.zone/read-manga/pet_keiyaku/
Also this:
http://www.mangago.zone/read-manga/toshishita_kareshi_no_renai_kanriguse/
And some djs:
http://www.mangago.zone/read-manga/shingeki_no_kyojin_dj_what_s_yours_is_mine_and_what_s_mine_is_my_own/
http://www.mangago.zone/read-manga/shingeki_no_kyojin_dj_kare_no_te_no_uchi/ (doesn't have bondage, but it's pretty d/s)
Oh, and since you said it doesn't need to be yaoi, Nana to Kaoru is a must if you don't mind ecchi.
http://www.mangago.zone/read-manga/nana_to_kaoru/
I'm guessing you've probably tried searching the BDSM tag here, but what about at bakaupdates? They have advanced search by genre and you can include and exclude any category. They'll have a lot more to suggest, including hentai (which obviously you can't really find here in a huge amount), since they don't actually have mangas, only information on them.
Pulled an all nighter to finish this one. I literally could not stop.
I'm so glad it had a mostly happy ending.
And is it just me, or did I feel *something* between Ayumi and Miki?
Haha their relationship felt VERY romantic to me, idk it's all up to interpretation.