This story contains multiple character deaths. There's a reason it's called Doomsday. And not just because it crosses with the episode of Star Trek: The Original Series called "The Doomsday Machine". Which I don't own. I don't own Buffy either, nor any anything to do with those two franchises. So don't sue me!
Although this story doesn't technically hit all the criterion of the "Ship of the Line" challenge, it hits enough. At least as many as some other stories which I could name.
Ever since they were little, Xander, Willow and Jesse had always dressed up as characters from the same franchise.
They'd gone as Star Wars characters (Willow had made a striking Chewbacca) X-Men (Jesse had even managed to get a hold of a real wheelchair, ensuring that they got plenty of sweets) and once, when Willow was feeling more than usually girly and Jesse and Xander couldn't talk her out of it, as various differently dressed Barbie dolls. That had been an interesting year.
They'd planned to do Star Trek this year, but Xander just didn't think that would happen. Not now that Jesse was dead. Willow hadn't talked about it, and Xander certainly wasn't going to remind her. No, if Willow was going to get over Jesse's death by forming a new tradition, there was no way that Xander was going to interfere with that.
That said, Xander didn't want to completely abandon the Star Trek idea. It was his own way of commemorating Jesse.
Xander had spent the last few weeks saving money for a costume, but he couldn't afford one from Party Town. Not that that was very surprising - that placed catered to the Cordelias of Sunnydale. It was no place for Xander.
Normally, Jesse's mom would've bought the costumes, but she'd moved away after the death of her only son. Xander couldn't blame her for that. But, unfortunately, it still meant that Xander had to get a costume somehow.
He couldn't ask his parents, they'd be too drunk. Nor would Xander ask Willow's parents - they simply didn't care about Halloween, and would probably be out of town in any case. Anyway, if Willow heard about it, it would only remind her of the years-old tradition that was now broken. Xander didn't want to do that.
Not before Willow saw him in his costume, at least. Assuming, that is, that he could get one.
So, when Ethan's opened, it seemed like a godsend. It catered to an entirely different clientele to Party Town, and even had some affordable costumes.
Xander politely declined both Willow's and Buffy's invitations to go shopping with them. He thought Willow understood when he refused, although she didn't say anything. For Buffy he'd spun some spiel about it being bad luck to see a woman's costume before she was out Trick-or-Treating. She seemed to buy it.
Xander had planned to be Captain Kirk this year. Jesse would've been Chekov - he was the only one of the three that could do a creditable Russian accent - and Willow had fought tooth and nail to be Spock, despite the boy's arguments that she should really be Uhura, or perhaps Nurse Chapel. Not that they'd tried too hard - both Jesse and Xander thought that Willow would be adorable with pointy ears.
Unfortunately, while Ethan's did have a captain's uniform, it was just a little out of Xander's price range. As were most of the other Star Trek costumes.
Not all of them, though. Xander dismissed the female uniforms out of hand - he'd already gone through that as Barbie - and didn't particularly want to be a Klingon. To Xander, they seemed too similar to vampires.
By a process of elimination, Xander was left with only one possible costume. A Commodore. It wasn't too dissimilar to the captain's uniform, and all in all, it seemed like the best choice. That is, if Xander didn't want to dress as something else entirely, which he didn't.
So Xander bought the costume, not paying much attention to the Englishman who worked the till. Xander's thoughts were filled with the memories of the friend he wasn't spending Halloween with.
It was with some surprise that Commodore Matt Decker found himself on a planet. The last thing he remembered was...
His ship, damaged. Beaming down his crew to the planet for safety, then watching, powerless, horrified, impotent, as that... thing, that devil had torn the entire planet to rubble, killing his crew. He'd heard their screams through the communicator. He could still hear them, even now, hours - days? Months? - after they'd stopped.
Had Decker lost his mind, then? He couldn't possible be on a planet. The transporter was broken, and besides, the remaining planets were uninhabitable.
How could you tell if you'd lost your mind? Decker couldn't. Everything seemed so real. The people, the buildings.
Okay, maybe not the things resembling goblins, demons, creatures from fairy stories. Maybe Decker had lost his mind, after all.
Decker didn't care. Perhaps it would give him a new life, a chance to start over. Atone for his actions.
Or at least, he could do that if that thing, that monstrous ship, hadn't come here with him. Decker looked up instinctively at the night sky, hoping, praying, that it would be empty of everything save for the stars.
It wasn't, of course. Decker was far too unlucky for that. That thing, shaped like a giant worm, maw gaping, revealing the fires of hell that burnt deep within it, floated above the town like the wrath of Heaven.
Decker didn't scream when the tractor beam descended, although all around him did. He welcomed it, welcomed the chance to rejoin his crew.
Decker spread his arms wide and closed his eyes, smiling beatifically at the Doomsday Machine.
Then he was torn to shreds.
Far away from the now destroyed town of Sunnydale, Ethan Rayne stood panting, and silently swearing in every language he knew.
He had portalled away the moment that ship had appeared in the sky - as a disciple of Janus, God of Doorways, he had that power - but it wasn't far enough. Nowhere on Earth would be far enough.
Ethan might have gone a bit too far with this spell. Just a little bit. Okay, a bit. Maybe a big bit.
Oh, who was he kidding? He'd caused the end of the world! Accidentally!
It didn't take long for the Doomsday Machine to rip the Earth to pieces like so much wet paper. It didn't take long for it to convert the rubble of an entire planet into fuel.
Then it moved onwards, seeking new planets to destroy. The ultimate Doomsday Machine. There was nothing to stop it, here. It would just continue, destroying and eating.