Hard Yaoi

http://www.mangago.me/read-manga/you_re_my_loveprize_in_viewfinder/

This is as hardcore as I can think of XD

Also forgot this one:

http://www.mangago.me/read-manga/hogu_hagyeongsu/?av=2

From Abe Akane:
Nigai no Theme-> http://www.mangago.me/read-manga/nigai_no_theme/

From Harada(I would kategorize all of her/his work as hardcore. I choose this two, because I favorite them-especially yatamomo):
Yatamomo-> http://www.mangago.me/read-manga/yatamomo/
(prequel:Sumomo- http://www.mangago.me/read-manga/sumomo_harada/)
Yoru To Asa No Uta-> http://www.mangago.me/read-manga/yoru_to_asa_no_uta/
(sequel:Yoru To Asa No Uta EC-> http://www.mangago.me/read-manga/yoru_to_asa_no_uta_ec/)

From Michinoku Atami:
Iyayoiyayo mo kiss no uchi-> http://www.mangago.me/read-manga/iyayoiyayo_mo_kiss_no_uchi/