You don't know what Bongo and the Chaos Warband have said to each other, or even how long they've been communicating.
DICK. Can we shoot that guy into the sun? He's really not that useful and now he pulls this? Burn in nuclear fire, dude.
Some analysis tells you that the enemy seems to be prioritizing the protection of specific boarding craft over others - they're more heavily armored. Blacker. Spikier, and hidden in the middle of the enemy formations.
Oh poop. Marines.
The enemy ship is doomed, but a teleporter signature betrays their final ace in the hole as a dozen heavily armored figures materialize near Bongo's Oubliette. They're eight feet tall and wearing familiar armor, though it's black and gold and decorated with horns and sigils of Chaos instead of the red-and-gold & aquilas of the Knights of the Crimson Vigil. Some of them bear visible mutations, with clawed armors or helmets partially hacked away to allow unnatural growths to protrude.
Naturally. The emperor makes one super-soldier race and all of a sudden they're everywhere.
Both sides open fire as one, and Cia is only spared from the resulting massacre by her void shield deflecting the fire that spills her way. Both of the other marines are torn apart but the leader of the Warband miraculously plows through the wall of fire. His armor is blackened with char instead of paint and the side of his face fizzles with the heat of a melta round that blew half of his helmet away but he's still mobile, and Cia's the only thing that stands between him and Bongo's vault.
Showtime.
Once more the Chaos Champion is tossed across the deck, smoking from a fresh application of fire. But this time Cia doesn't pursue and instead gives a command you've been waiting for. "Fire."
You oblige, pouring the full weaponry of the thirty combat bots that have arrived during the duel into the enemy leader. He evades and survives far more of the shots than should be possible, but after thirteen plasma rifles, five melta guns, and two rockets are all emptied into him he collapses, more of a swiss-cheese of armor than anything else.
HAHAHHAHAHA. Honor duel that, poser! I love that bit in fiction where the second theres a lull in a melee fight one of them just gets shot to peices.