This story begins during the Buffy season 5 episode "The Replacement", and takes place roughly during the same season of Stargate SG-1, neither of which are programs that I own, nor will I ever own. So don't sue me.
This is part of my series "Scoobies & Stargates", which you will need to have read in order for this to make any sense whatsoever.
Dawn had been feeling more than usually smothered lately. It was really getting on her nerves - after all, she was fourteen now, nearly the same age Buffy had been when she had been called, and she had already known about the supernatural world for years.
Of course, Dawn had understood why Buffy was smothering her. Dawn had been content to stay out of that world, before. When Dawn had first found out about it, she had found that Angel, the man her sister had been sort-of-dating, had turned into a mass-murdering psychopath intent on destroying the world. That kind of thing really puts an eleven year old girl off the idea of magic and monsters.
Then, when it turned out that the Mayor had been planning on turning into a giant snake and eat Sunnydale, Dawn had been more than happy to stay out of that one, given her fear of snakes, giant or otherwise. Besides, there wasn't a lot she could've done about it, so she and Joyce left town on graduation day.
Things began to change after that, though. Especially when Dawn had tagged along with the group and SG-1 (how cool was it that Willow was off exploring the galaxy and fighting aliens!?) to go and put an end to Caelus' nefarious scheme to open the Hellmouth. He'd chained Dawn up just like the rest of them, even knocked her out for talking too much.
It had really been driven home to her when Willow had told her about helping to destroy a giant spaceship (after getting over being possessed and then kissed back to life by Daniel) that she could actually make a difference. Of course, Dawn was way too young to join the SGC, but she could help with the magical stuff. But Buffy didn't understand that, she just wanted to keep Dawn out of it. Hence the smothering.
So, when Giles had called Buffy to tell her that he had been attacked by some kind of demon that had been looking for her, Dawn pestered her sister unmercifully until Buffy had a choice between tying Dawn up or letting her come with her. Given that Joyce would be furious to come home and find her youngest daughter tied up, Buffy had no choice but to let Dawn come along.
Of course, Buffy spent the journey to the Magic Box telling Dawn exactly what she could and couldn't do - which boiled down to "Stay still and do whatever I tell you".
Dawn snorted inwardly. Yeah, like that was going to happen.
Dawn wasn't really all that surprised that Giles had been attacked before the Magic Box had even opened. Giles got attacked and knocked out more than anyone she knew, and having seen the last owner of the shop, Mr Bogarty, sprawled dead on the floor - Dawn had seen way more than just a foot - she knew that the owners off the Magic Box had the highest mortality rate of any shop owner in Sunnydale, which was saying something. Giles and the Magic Box was a bad combination.
On the other hand, as Giles had said, he wasn't unconscious so it was a win for him.
It didn't take Giles all that long to find out who the demon that had attacked him had been. Toth, of the Tothric clan. Dawn absently wondered if he had a brother called Rick, but she didn't say it out loud. Although Xander would probably laugh at it - which was good - Buffy would probably think that Dawn was being silly and make one the other Scoobies take her home - which was bad.
As the other Scoobies loaded themselves with weapons, in order to hunt down Toth, which Giles' nose suggested was lurking in the junkyard, Dawn couldn't help but notice that she was conspicuously weaponless. She supposed that she should be grateful that Buffy hadn't sent her away. Although that was probably because she had forgotten Dawn was there.
Upon reaching the junkyard, Dawn began to wish that she hadn't been quite so insistent on coming. It really stank. Really, really stank. Worse than using the bathroom after Buffy. Which Dawn had only ever done once and had sworn never to do so again. That was how bad it was.
But, if Dawn was going to make a difference, she should be able to put up with things like this. If Buffy wasn't stopped by dying, Dawn wasn't going to be stopped by a truly awful stench.
Or by Spike rummaging around the heaps, apparently looking for furnishings for his new crypt. Dawn felt that, besides Willow and the other members of SG-1, she was the only one who actually accepted that Spike was no longer the Big Bad that he still occasionally claimed to be. The others still thought that he was a serial killer held in check by a chip in his head.
Hence Buffy being somewhat peremptory in asking the vampire whether he had happened to see Toth. Dawn wondered if she was the only one who noticed how tired
Spike looked as he wordlessly pointed behind the group.
All thoughts of Spike were driven out of Dawn's head as blasts of some kind of energy flew through the air, mercifully missing everyone as the group scattered from the hulking figure of the demon Toth.
Dawn noticed that, besides making a bang erupt some feet behind the various items if rubbish Toth hit, the weapon he was firing seemed to do absolutely nothing. Maybe it only worked on living things?
Buffy quickly realised that she had to change her battle plan. It probably wouldn't be a good idea to be hit by a bolt of the energy that Toth was firing, which meant that she had to keep her distance and keep moving. Unfortunately, she hadn't brought a crossbow, so she had to improvise. Buffy pulled a knife from her sleeve, hoping that it was a throwing knife (she had several on her person, but at this moment she wasn't entirely sure which was which) and hurled it at the demon.
Even as the knife spun end over end, hurtling towards Toth, so too did an energy blast streak it's way towards Buffy.
Buffy, off balance from hurling the knife, didn't have enough time to move out of the way. Dawn could see Xander making his way to Buffy, but she could tell he was too far away. Dawn, as the nearest, was the only hope.
Even as Dawn ran towards her sister, she could tell that she was moving too slowly, that she wouldn't make it in time, that the blast would hit Buffy.
Then Dawn must've tripped over something, as she suddenly was moving rather faster than she had planned. She cannoned into Buffy, sending the Slayer sprawling even as the bolt of energy hit Dawn right above her heart.
The bolt went right through Dawn, and it seemed, if anything, to be even brighter than before, incandescent, a blinding, amorphous blob...
Dawn collapsed unconscious and the blinding light vanished. It took several moments of frantic blinking before any of the Scoobies could see anything, but when they could they wasted no time in picking up the prone Dawn and taking her home, pausing only for Buffy to pull her knife from Toth's head and pick up the curious, tubular weapon he had been firing.
Elsewhere, at that very moment, beneath Cheyenne mountain, SG-1 was preparing to head through the Stargate on a routine meeting with their Tok'ra allies. Sam was looking forward to seeing her father again, and Willow was looking forward to meeting him for the first time.
It was a perfectly normal mission, nothing out of the ordinary. None of the technicians read any anomalous energy readings whilst the 'gate was active.
So, no one understood why, moments after heading through the 'gate, SG-1 came back through and collapsed on the ground. Nor why, moments after that, SG-1 (save for Daniel, oddly enough) came through the 'gate again
, and fell unconscious upon the bodies of... themselves.