http://www.mangago.zone/read-manga/zettai_fukujuu_meirei/ only one i could think of but it fits the narrative. enjoy!
There is Scandalous M although it isn't the seme who introduces the uke to his submissive side.
But the seme is a real sweetheart in this one
Hi! Here are some good ones:
http://www.mangago.zone/read-manga/blood_bank/?N7KC
http://www.mangago.zone/read-manga/my_partner_s_tastes_and_fetishes/
http://www.mangago.zone/read-manga/alien_in_my_closet/
http://www.mangago.zone/read-manga/whatever_the_start_may_be/
http://www.mangago.zone/read-manga/aplicaci_n_humillante/
http://www.mangago.zone/read-manga/tempters/
http://www.mangago.zone/read-manga/scandalous_m/
http://www.mangago.zone/read-manga/from_points_of_three/?7zXh
http://www.mangago.zone/read-manga/private_lessons/?iTTO
http://www.mangago.zone/read-manga/ang_ang/
http://www.mangago.zone/read-manga/the_double_life_of_the_demon_king/
http://www.mangago.zone/read-manga/master_of_master/
http://www.mangago.zone/read-manga/sm_gokko/
http://www.mangago.zone/read-manga/puppy_love_eumnya/
http://www.mangago.zone/read-manga/make_me_bark/?dFUd
I hope this helps! <3
http://www.mangago.zone/read-manga/sakurada_senpai_kaizou_keikaku/ (Kinda a weird story but I find it pretty funny with rlly smutty sex scenes)
http://www.mangago.zone/read-manga/my_partner_s_tastes_and_fetishes/
http://www.mangago.zone/read-manga/simplified_pervert_romance/?HyEz (The uke in this one is a super M... like he picks fights cuz he wants to be hit. It’s a pretty good story overall)
Can anyone recommend smutty yaoi where the uke is a masochist, but the plot isn't too dark? extra points if the seme introduces the uke to his submissive side without being too rapey >-<