Let's see if I can list a few ways it goes down:
For rape, we have:
Rape: Raids on settlements, caravan's, hostage ransoms, slave trading, Spoils of war, BBEG Dark overlord breeding programs or otherwie secret breeding pits when there is need for greater numbers of orcs bordering into Daemoncubla tier stuff, Political negotiation rules lawyery into rape, prisoner for whatever reason rape Mass immigration rape, forced and rushed recruitment in war efforts with mercenary groups with vulnerable units taken advantage of and given a blind eye too.
Orc customers in a not so legal house of pleasure, and good old mind control, hypnotism and drug abuse.
Lastly, possesion by higher or lower forces driving them to fuck orcs, and lovers subject to experimentation or polymorph bullshit fuggin their loved ones.
For reluctant/forced we have:
Political marriage, Peace offerings, and arranged marriages in general, Prostitution (either way) raised by orcs until womanhood where they stay their hands no longer on claming the booty and fleeing isn't exactly and option and whatnot, sexual/love interest transformed into orc and he has a horny level that needs to be satiated, drug abuse and alchohol, subject of sex is on an incredible dry spell/in heat because animal person, breeding experiments (Subject may be higher up than just slaves or captives and may be the experimenter themselves) Chaste Religious idiot being taken advantage of, or Orc trickery and grooming through private out of sight encounters in a cave with generic troubled village loli who no one takes notice of, or lower class citizens under some opressive orc rule. We've also got destined child unwanted by the mother,/orc demigod/reincarnation shit
For consensual we have:
Legitimate love, grooming, part of an orc orc cult (or requires a cult) with hot sexy sex rituals, Orc jizz has magical properties must aquire, Dry spell neglected females/low fertility rate desparation, slutty elves and slutty naked elves and orcs that run around the forestplaying sexual tag or sothing that absurd, part of a harem whether the harem master is female (drow) or male, whatever, is the only good looking orc in the village and is snu snu tier, Alchohol resulting in orgy or morning after and a shitload of things have been fucked, Orc is a prostitute, Orc is a male stripper, Orc is a bard, Orc is subject toMasterful cuckold interracial NTR propaganda and get's to fuck brainwashed wommens and the like, Rape/forced into consent via stockholme syndrome (Though that definition is very loose because sometimes it's true love through brutaity or some shit)
Magical orc jizz, phermones, or sexualizing mind controlling spores, Unavoidable Orc Demi god creation process, reincarnation and malevolent reincarnation (Micky Roa my boat vladonmydingdong)
This covers a few things.
Oh right, and everything that would apply in normal situations in the case of half-orc fucking and orc or just other people