So uh
Thanks to the acoustics of the mostly empty cargo hold, Boris could actually hear the tired sigh that followed Medenov's outburst. "Just tell me the yield I need to use. And initiate, pick up bodies gently so you don't leave incriminating drag marks, and make sure you don't bruise them. Because AL-Loy clearly has a forensic analyst who is going to look at all three grams of recoverable tissue and wonder why there's bruising."
Another hiss of disgust. "Initial shell impact from an AL-Loy light defense boat... 1.324 million newtons."
The Fin was clearly cybernetic, and had some form of anti-gravity gear integrated into its body. He floated up at about 75% of room height, carefully placing a box shaped explosive charge on the bulkhead.
"I mean, I'm over here, and you're down there, so it'd be a bit impressive if you could crush my skull. Not that I'm asking for an example," the Fin added quickly, hovering a little higher, "but, uh, anyway... First answer. There's probably a half dozen actual troopers left on board, plus as many initiates. Then there's the officers, and the... unconventional units. So, maybe like fifteen, seventeen sapient creatures and three or four more dangerous but less sapient critters? Too many for you, and it'll be just as bad if they decide to start sending people down here rather than you coming up."
You have an explosive, and there's some chance it's a shaped explosive since it's supposed to be replicating a cannon shot, that's currently set to- but might be able to go higher- than a light ship's cannon. If fired directly into, for example, a line of soldiers coming down a narrow corridor to murder the shit out of some intruders, it might be very effective. If fired into, for example, the access hatch of a ship generally intended to tank shots with its outside, it might also be very effective. If both of these are true and we're very lucky, it might be laughably effective.
It could also not, in any way, be a shaped charge, and thus unable to do any of that without ripping the ship you're in asunder or being placed directly in the murderer-infested corridors you want cleaned of murderers.
The Fin made several incoherent sounds of disgust and horror, using his harness arms to wipe off the larger chunks that were sticking to him. "Oh.. blyecch! Control! Mercenaries have infiltrated, send a cleaner, I repeat, SEND A CLEA-"
Boris cut him off with a hundred pound cargo crate, smashing the fin upwards into the ceiling. There was a spark from his exposed cybernetic, then he hit the ground with an only slightly dampened splat.
"... Ow... Would you... be so kind as... to give me a minute so... so I can reboot... a couple things?"
The little blue lights, however, did not fall with the fin. They continued to fly up, touching the top of the cargo hold. There was a single bright spark as they connected, then they fell to the ground with a metallic tinkle.
"Request Acknowledged, Sarraki. Sending a Cleaner."
The new voice, full of static, was audibly piped through from Sarraki's rig. At the same time, a panel in the ceiling clicked open. I looked like a normal interior plate that someone had cleverly cut in half and then reassembled. On the other side was what looked rather like an airlock.
For a simpler but riskier plan, you could arrange the Fin such that he's visible and alive but unable to speak (mouth crammed full of bobbleheads, perhaps?) and placed in a convenient ambush location. When the Cleaner arrives, whatever that is, it investigates the Fin and is ambushed by its actual targets.
Of course, if the Cleaner is a unit of troops rather than an individual, that could be bad. If the Cleaner is too tough to ambush easily, that could be bad. If the Cleaner knows not to eat friendlies and can sense hiding Kings and Crows by smell, that could be bad.
For a third and even less likely plan, you could try to draw more enemies deeper into the freighter, then set off the charge and storm the Nosoi. Boris could hide in a box of stuffed animals, Kesari could use her invisibility, and some wedged or hacked doors could give the impression that you're holed up deeper than you are. You might need the fin's cooperation (or defeating their half-measures) in getting them to stuff all of their valuable assets down here, though.
For a fourth and more likely plan, you could
actually hide on the freighter and wait for the Nosoi to dock, at which point their forces will be split (and wrecking the Reunion's shit). Assuming they don't just dump and destroy the freighter en route, which is... quite likely, actually!