Black Legionnaire with a magic gaydar that lets him know which Space Marines would like to receive a pussy and become pregnant (so then he kidnaps them for their own good).

The gaydar isn't 100% accurate and he altered a Space Marine who will never accept having Chaos babies with his new husband (perhaps they do want to be pregnant, but never like this).

This Space Marine's behaviors makes him a danger to the other breedable Space Marine he's housed with (communal housing because Space Marines are social animals and raise each others' children) so he must be done away with.

But Space Marines are terribly expensive to acquire, and keep alive. The Black Legionnaire has a sunk cost fallacy. He can't just kill this one when he's spent a fortune keeping him alive.

So the Black Legionnaire has the offending Space Marine sedated and taken away by a medicae team and tells the remaining wives "he has been rehomed" and "sent to live in a coliseum somewhere to fight daemons" (equivalent of saying you sent an old animal to live on a farm when you're euthanizing them).

This naturally causes more panic and fear among the wives than if the Black Legionnaire had him publicly executed and made the wives attend the public gathering (a Chaos marine must keep their followers happy with bread and circuses, and killing the horrible corpse worshipper who hates all that is good is the circus part of the equation).

Surely, he must have been lobotomized and is being bred back to back in a dingy cell somewhere. Or slowly sold for parts. Or sold to a Drukhari. Or if he's dead, stuffed and turned into a table decoration in a mansion somewhere.

If he'd been publicly executed, at least his death would be swift and he could no longer be used by the enemies of the Imperium in increasingly undignified ways.

The truth is the most unbelievable: the Space Marine really was sent to a coliseum to be its star gladiator after the coliseum owner paid the Black Legionnaire a hefty sum. He's doing what he loves now: fighting.

Secondborn Black Legionnaire humping away at his captive Space Wolf bride like a dog, mounting him from behind, trying to knock the Space Wolf up. Transforming into a giant, fluffy dog monster and knotting the Space Wolf once he's shot his load, to ensure the Space Wolf has the highest chance of getting pregnant.

The Black Legionnaire gropes the Space Wolf's round tits and generous belly. All that fat is good for nourishing pups.

The Space Wolf is made to howl and howl when he orgasms.

The Space Wolf glares at him in a moment of post-nut regret, feeling degraded, trying to pull away from the knot so he can sulk in peace. The Black Legionnaire tries to reason with the Space Wolf. The Space Wolf has extra sets of nipples and surely would have been euthanized by his legion if the Black Legionnaire hadn't stepped in and "rescued" him. He has a place to sleep and a place to belong, in a mansion with all the other pregnant Space Marines. Is it really so bad? He shouldn't be ashamed of feeling pleasure.