I haven't read Lady K in a looooong time so I can't remember just how hard-core it was, but, these are some of my favorite het smut
Tada no Renai Nanka de Kikkonai -Kojirase Joushi to Fechina Buka-
Otto Wa Watashi Ni Mainichi Maiban Oboretai (there's 3 or 4 oneshots in this series)
Sumi-iri Osananajimi no Sokubaku ga Tsurai
Last Order wa Ojou-san de Dekiai Jouren Kyaku ni Kyuuai saretemasu
Yuusha Party kara SEIJO wo Sukutta no ha MAOU-sama Deshita
Gobbling the Goblin
At This Rate, We Can't Be Best Friends
One of my lists. Pretty sure they're all consensual.
https://www.mangago.zone/home/mangalist/2625040/?filter=&page=1
https://www.mangago.zone/read-manga/if_i_have_a_chance_i_want_to_warp_my_boyfriend_s_fetishes/ idk if you're into healthy femdom but I'll drop it here just in case
any straight smut that isnt like rape or a power imbalance but also hardcore?? LIKE LADY K (b4 the tentacles ofc)