ooh, I'll do jjk specific followed by gen:

any and all mob/side charas x yj, including ko-guy 🖤

and then in gen:
ult. 5 x hatori from mp100 (iykyk), jaguar x piyohiko from Pyu! To Fuku Jaguar (again, iykyk), mob older women x alibaba from Magi

and lastly, some super old school honorable mentions are one-sided kevin x husky from +Anima, and radu x ion from Trinity Blood (manga only!!!)
they're only mentions because both are just served on a silver platter in canon LOL