ff
What does Op mean?
It means over-powered (⌒▽⌒)
one punch man
Then I recommend
http://www.mangago.zone/read-manga/saiki_kusuo_no_sainan/
but I am not sure it is the kind of Op you are looking for (=・ω・=)
But it is funny as hell.
ff
Op MC manga with no romance or harem at all. . I can't seem to find any besides Solo Leveling or King's Avatar