If I remember correctly, all 3 stories in Pheromone Shower have that pairing.. Tho the last story is the best imo..
http://www.mangago.me/read-manga/pheromone_shower_omegaverse_short_stories/
http://www.mangago.me/tag/omega%20seme/ First three are also like that as I remember
I've been wanting to share this manga to anyone!! It's called Boku no High Spec Kareshi-sama and it's hilarious aff
http://www.mangago.me/read-manga/boku_no_high_spec_kareshi_sama/
hope you enjoys this as much as I did :))
are there any top Omega , bottom alpha BL? (Like the omega puts it in)