Hello, and welcome to my first crossover, A Gem's Determination. This takes place in an alternate universe in which the Cluster has been destroyed, and in that AU, Peridot sacrificed herself to get the rest of the Crystal Gems to safety. However, Yellow Diamond made her appearance known to them, and had threatened to come to Earth to wipe it out herself, basically declaring a second war between the Crystal Gems and Homeworld.

So, there's spoilers for episodes involving Peridot and the Cluster Arc, mainly involving episodes that happen during this Stevenbomb(Number 4), so be careful if you haven't seen those episodes yet. If there's heavy episode spoilers in a particular chapter, I'll probably put that in the author's note in the beginning of that chapter, too.

Also, tons of spoilers for Undertale, here! If you have ANY interest in the Genocide/No Mercy route and have not played it/watched it, GET OUT NOW. And no spoilers in the reviews, either, I don't want to ruin anybody's experience of watching Steven Universe or playing/watching a let's play of Undertale. Normally I don't do this, but since both this show and game tend to get spoiled quite a bit on the Internet, I just want to make sure that it doesn't happen here.

Well, now that's out of the way, here's the full summary, in case it doesn't fit:

Summary: Connie falls into the Underground while training one day, and the Crystal Gems follow suit to bring her back up to the surface. However, an unexpected event makes it exceedingly difficult to find her, and an unexpected appearance threatens to trap them all down there, unless they can find a way for Determination to be used to change everything...

I hope you enjoy the story!

Steven Universe belongs to Rebecca Sugar and Cartoon Network. Undertale belongs to Toby Fox.

Prologue: Fall

The legend of Mt. Ebott was quite a strange one to the populace of Beach City, which was saying something, because Beach City itself was not the most normal place in the world. Rumor was that there were strange monsters living in the mountain, with properties similar to Gems, but lacking in any human feature. It was also said that they were sealed inside the mountain by the Gems long ago, with a powerful magic keeping them trapped inside. However, nobody ever went to investigate. A few teams in the past did, but none never returned. Now, in Beach City lore and cautionary tales, lies Mt. Ebott, a place where people go to, but never return from.

All fear it, with the exception of the Gems.

The Gems is where our story starts, in fact, a story of loss and being found, violence and virtue, and revenge and forgiveness, as well as love and determination.

Huh? Lost already? No worries, all will be explained in due time. Be patient.

Who am I? Well, that's a secret. Just know that I'm nobody important.

Why and how am I talking to you?! Well, well, someone certainly asks a lot of questions! Why can't you just enjoy a story? Stop questioning everything and just enjoy this tale, alright? Anyways, our story starts with the Crystal Gems...

Stevonnie took a few deep breaths, hiding behind a tree. They tightened the grip on Rose's sword, a grip that was already shaking, not just from the stress, but also because Steven had to stop summoning his shield so they still could be together as one.

"You're doing fine, Steven." Stevonnie said aloud, but quietly, looking around for any of the Gems. Connie knew that it had been the longest Steven that had summoned the shield before. He clearly needed a break. "Are you sure you want to keep going?"

Steven took charge again and nodded. "You know we can't stop for anything." A flash of light and Steven's shield was back hovering on Stevonnie's right arm. "Let's keep moving. Garnet's probably planning an attack now with her future vision, and who knows where Opal's at."

This was their idea of training for Yellow Diamond-fusion drills, they called them, and was basically close combat training with different fusions. This time, it was Garnet and Opal versus Stevonnie, with Stevonnie representing the Crystal Gems-in case "anything went horribly wrong," Pearl reminded them. It always worried Steven whenever Pearl said that. But, he knew why.

Any of them could end up like Peridot in the heat of battle. Any of them could easily end up being shattered.

"Concentrate, Steven." Connie warned, taking control again. "Let's head north. If we can find a vantage point, we might find Opal, which is good, because melee fighting's her weakness, since her weapon's a bow."

Stevonnie left the safety of the thicket without another word, sheathing the sword, but holding the shield close to them. At that moment, there was a loud thud behind them, and Garnet lunged towards them. Stevonnie casually moved out of the way, their expression blank, and quickly hit her torso with the hilt of the sword, leaving Garnet on the ground, unhurt but slightly winded.

Opal fired an arrow from where they were, nearly hitting them, but Stevonnie easily sidestepped it and continued on, slamming Garnet back on the ground again with the blunt side of their sword. Opal fired a quick barrage of arrows at them, and they quickly continued north, where the forest was thicker, Garnet close behind, and Opal still firing at them.

Stevonnie, still sidestepping arrows from the sky, zigzagged through the woods, hoping to lose track of Garnet along the way. Opal was finally visible, leaping through trees and making quick barrages of five or six arrows before continuing. Garnet managed to circle around them, and threw down her gauntlets, causing a rift in the earth. They ran off to the side, then lunged at her, pinning her to the ground and holding the sword to Garnet's neck.

Opal dropped down from where they were, defusing and Pearl running over towards them. There was nothing but the wind, and the silence was deafening.

"Something's wrong." Garnet said softly. "The ground shouldn't have broken like that here." She gently pushed the sword to the side and stood up. "Steven, what's going on? Can you regain control?"

Stevonnie looked shocked for a moment, then stepped back, getting into an attack stance. At that moment, they unfused, Steven jumping towards Garnet, but Connie standing still. The ground broke under Connie's feet, and everything moved in slow motion, a look of confusion quickly turning into shock as the rocks and dirt underneath her feet slipped away, and she fell backwards, her mouth opening in a scream, her hand outstretched. Steven reached out his hand, and felt her fingertips brush against his as she fell down into the depths below.

"Garnet, is Connie…?" Steven asked, staring at the gaping hole in front of them.

"She's fine." Garnet said, looking back at the other Crystal Gems. "However, she's fallen into the Underground. It's going to take a while for us to be able to get her out. We should head back to the temple for now and gather supplies. It's getting late."

As Pearl and Amethyst followed Garnet back to the Warp Pad, Pearl gently tapped Garnet's shoulder, making sure that Steven wasn't too close behind.

"He still doesn't remember what happened." Pearl whispered. "If we go down there, he's going to want to go, too. But, if he does, then…"

"That's a risk we're going to have to take, Pearl." Garnet whispered back. "He was bound to find out eventually, anyway. I just wish it wasn't like this. But, either way, I'm not looking forward to going back there, either. The monsters hate Gems."

"Yeah, and if they didn't hate us, they'd hate humanity." Amethyst added in. "Or, maybe just hate us even more. We did do the right thing, though, right?"

"Yes, Amethyst." Pearl said tiredly. "We did do the right thing. We did what we had to to keep them safe. Let's hope we can do the same for Connie, as well."