Despite its reputation as a region historically safe from Gem-related events, the Midwest had in fact been the site of a number of Gem-related events. In contrast with its safety, it had a higher-than-average concentration of cryptids and myths passed down through folklore - all of them misidentified Gem Monsters, naturally. This was due to the the region's status as a colony ship parking lot of sorts during the occupation, the circumstances surrounding the hasty evacuation of Earth at the end of the Gem War, and what happened immediately afterwards…
The Crystal Gems had been instrumental in securing the region for Human repopulation. They defeated some monsters - generally the most aggressive ones - and sealed others in their ships, then piloted them deep under to prevent future exploitation and accidents. Pearl herself had personally decommissioned most of them on her own, in fact, and occasionally checked up on the region to make sure they stayed underground.
That had worked so far. And then the blue and green brats - the 'peacock pair' - figured out a new way to annoy her. Worse, they managed to do it directly underneath the heavily populated Kansas City, by finding a ship and then digging a tunnel down to it.
Pearl scraped the rock-and-earth wall of the tunnel the drone had led her through. It was just tall enough for someone her height, and crumbled in a way that confirmed what she'd expected: Peridot had likely gotten Lapis to use her water powers to drill out the tunnel (after somehow working out where an unexplored ship was). "You both know better than this," she said to herself.
She caught up with the drone waiting for her at the solid end of the tunnel, emitting enough light to serve as a beacon even in the all-swallowing darkness. There was an access hatch there, clearly that of an Era 1 Gem ship, cleaned off and recently used. If the drone had fingers it would have pointed at the hatch, desperately trying to be useful.
"What's wrong with this picture?" Pearl asked herself. The situation made sense on paper - the brats had gone exploring and gotten stuck - but there was something off about it all. It didn't feel like the sort of place either Peridot or Lapis, homebodies extraordinaire, would go out of their way to enter on their own. In the back of her mind there was a little voice telling her that it might be a trap, a subconscious reaction to some minor detail...
Ah. That's what it was, Pearl realized. It all felt like a thing Peridot might have done back when they were enemies. Two Gems, aligned with Homeworld until recently, were trying to get Steven to enter a wreck on their terms.
She shook off the thought and sighed. If her mind consisted of a parliament of Pearls, each representing a single aspect of her being, then it was time for Logical Pearl to tell Paranoid Pearl to take her seat. Even if It really was only a little while ago that they'd both agreed to live peacefully on Earth, they'd sworn to abide by its rules for Steven's sake. They'd earned his trust and, at the very least, weren't the types to betray a friend.
The access record on the screenpad next to the door indicated that the arrogant cactus and the indifferent water bottle were the only recent guests to the ship. And they'd only ever entered once, earlier that day. Steven's friends really were inside the ship, then, and they really had requested assistance.
Not from her specifically, but she was Pearl of the Rebellion! Vanguard of the Crystal Gems! The Terrifying Renegade! And the Eleventh Sanada Brave!
Pearl tapped a couple of buttons and opened the hatch. It was dark inside, as dark as the tunnel would have been without the drone illuminating it. "How about you?" she asked. "Are you coming in?"
The drone shook its front end left and right.
"All right. Leave and get help from the Crystal Gems, if things look dangerous. Wish me luck." She took one last breath of safe, tunnel-flavored air, and then took a confident step into the ship.
The hatch closed behind her, leaving the drone waiting alone.
The air was quiet and dry, and unlike Human ruins lacked even dust in which footprints could remain. A normal Gem colony ship of some kind, really. She'd activated her gemlight as soon as the hatch had closed, but all she could see were the walls and floor.
That was a problem. It meant that the spatial compression system was still active, making it considerably bigger on the inside than out, when it was supposed to be fully deactivated. Worse, there was no way to reboot and initiate the ship's generator in a short amount of time, and so it had to have been active for some time prior to Peridot and Lapis's arrival.
As she made her way deeper into the ship it became increasingly obvious what had happened. Most Gem ships had some sort of internal defense system, to hold off intruders until the crew could capture them. Peridot had once activated and suborned such a system against the Crystal Gems; there was no reason she couldn't do it again.
But they were inside a training ship. The high, decorated ceilings and sturdy halls, all of them built with neutral brown stone-like materials, were unmistakable. Training ships didn't have or need internal defenses, because they had training drones whose combat capabilities could be scaled up to severely high levels, indistinguishable from actual battle.
Judging by the broken training drones Pearl kept finding as she explored, Peridot or Lapis had managed to initiate a training scenario...
Suddenly Pearl heard a distant explosion, followed by a couple of smaller BOOMs that shuddered through the floor, all from an indistinct direction. "Uugh," she groaned as she produced two of her Bayonet Spiral spears, then prodded them into separate points on the wall and floor.
She didn't have to wait long. After a moment there was a third smaller BOOM, the direction of which she was able to triangulate with her spears. And with a quick, incidental analysis of the shockwave, she confirmed that it hadn't been caused by terrestrial explosive materials. "There they are." She retracted her spears and began running towards their source, unsure of what she was going to find.
...But ready to fight it if necessary.
Author's note: Things are going to speed up from here! There are going to be EXPLOSIONS and DRAMA.
The 'Eleventh Sanada Brave' and 'parliament of Pearls' ideas are things I came up with for other fics. Maybe I'll even finish them someday.
"Bayonet Spiral" is, of course, fanon. I made up some names for their weapons and a couple of attacks back in one of my older fics, to spice up a contest entry, and this is one of them. (I use Amethyst giving things anime-names as a running joke.)