I found this manga list.All credit goes to nanu-nana
http://www.mangago.zone/home/mangalist/43665/
http://www.mangago.zone/read-manga/yatamomo/
dunno if this fits your standards but yeah. Rather than size, the guy is totally insatiable so... Yah
Harada's Messiah (not one shot, the story has 3 parts)
http://www.mangago.zone/read-manga/messiah_no_yakubi/
And a manhwa If you Hate me that much
Also try to find La histiria de Hosik, it's funny omegaverse story.
ah sorry, not omegaverse, but similar
http://www.mangago.zone/read-manga/crystal_harem/ Here it is with the seme being a cop
Okay, last one haha. Maybe. Who the fuck am I kidding haha
I'm looking for any manga where the size difference is huge but....I'm looking for ones where they have a struggle during sex just because of the size difference. I've found maybe one or two that fall into that category but if anyone else knows of others...
Thanks ahead of time for any help provided!