(Before anyone gets confused, "Incomplete" is the AU's name, I didn't forget to name it after writing it)

What if Sabre had an incomplete soul, and was wandering through worlds to try and look for something that will make him whole? (Hey that rhymes)

 How that part would work is that Sabre literally has a ton of pieces missing from his soul, yet he is still alive and completely fine other than that. He doesn't remember when he lost those pieces, as it's been a very long time, but knows he can't get them back by now. Instead, he wanders worlds looking for something to replace those missing pieces. If he does find something, he can just absorb it entirely. Basically he absorbs anything he can get his hands on as long as it's not something that belongs or is important to his friends.

However, what he doesn't know is that absorbing things doesn't really work, and they're never completely absorbed for a very long amount of time (Like, the thing he absorbs stays a thing for like a month, then it's too late to get it back), so the things he tries to absorb to fix his soul can be taken back out (similar to how when Light and Rainbow fused to fight Chaos, they could separate). The things might disappear after a certain amount of time, but they never actually fix his soul, so Sabre is constantly looking for more stuff to absorb.

When Void tricked him into going in the tomb, Sabre wasn't scared like "That's a tomb, probably haunted, I shouldn't go in." Nah. He was like; "Ooh, a tomb, probably has some sort of powerful thing I can absorb." He only regretted his decision when Void closed the tomb in.

Throughout RQ, Sabre never absorbs the Crystals/Crystal, as while it is powerful he doesn't want to take away his friends' only defense against the Darkness. However, he does try to find a lot of random stuff to absorb, stuff he probably shouldn't be.

Situations to better explain what I mean:

(Orange Steve in the Rainbow Hub with Sabre before the Nightmare arc.)

Orange: Hey Sabre, want a pufferfish?

Sabre: Uh, sure?

(Orange gives him one, turns around to pet Gerald for a single second, and turns back to see that Sabre is no longer holding the pufferfish.)

Orange: Wha- Where'd it go?

Sabre: Where'd what go?

Orange: The pufferfish I gave you? I turned my back for just a second and you don't have it anymore?

Sabre: Oh yeah, uh...

(Sabre thinks for a little bit, but then Orange hands him another pufferfish to see what would happen. Sabre takes it, and Orange doesn't look away this time. Orange then sees the pufferfish suddenly dissolve, the remains glowing and sinking into Sabre's hands.)

Sabre: Oh yeah, that's what I did.

Orange: ...Sabre that's not what you do with it.

—

(Sabre and Orange training in the Hub.)

Orange: Hey, can you catch lightning bolts?

Sabre: I dunno-

Orange: Let's find out!

Sabre: Wait-

(Orange tosses down a lightning bolt and Sabre... catches it, the bolt turning into a ball of electricity. Then, Sabre absorbs it.)

Sabre: Oh, that wasn't so bad.

Orange: You... you just... absorbed it.

Sabre: Yeah?

Orange: That was a LIGHTNING BOLT. As in, just, TONS OF ELECTRICITY.

Sabre: O-Kay? Hey that was actually kinda fun, do it again.

Orange: ... Sabre, this is getting concerning.

—

(Darkness attacking Orange Village. Orange and Sabre are fighting in front of the Leader's house. A regular Darkness (not an infected person, just pure Darkness) starts running up to Orange.)

Sabre: ORANGE, LOOK OUT!

Orange: Huh-

(Sabre tackles the Darkness, and it's just instantly absorbed. Orange just stands there and stares at Sabre, as that was the last pure Darkness creature and the infected people are far away.)

Sabre: Oh cool, I can do that to them!

Orange: ...DUDE.

Sabre: What?

(Meanwhile, Void watching from the... well, void.)

Void: ...What the fu-

—

(At Nightmare's castle in the Yellow Kingdom, Sabre and Orange are getting rid of the fake Orange Crystal that could explode. Remember that Yellow Steve is there (He has a specific job but I forget). Sabre just picked up the fake Crystal.)

Yellow: Okay, now what? It could still explode.

Orange: I'm taking it back to our base and then destroying it-

(They hear a weird sound, and they look at Sabre just as he finishes absorbing the fake Crystal.)

Sabre: ...What? It's not a problem anymore.

Yellow: What in the name of-

Orange: SABRE. YOU JUST ABSORBED A FAKE CRYSTAL. THAT COULD EXPLODE. 

Sabre: Well, not anymore!

Orange: BOI-

Yellow: Is- is he gonna explode?

Orange: Wh- HOPEFULLY NOT.

Sabre: Nah, it fine, I've absorbed TNT that was about to explode before.

(Silence)

Orange: ...You've WHAT.

—

(Yellow Steve (leather chestplate, although he doesn't have that yet) showing Sabre and Orange the bunker he's been staying in, when he needs to shut down the generator so the door will close on the Darkness.)

Yellow: The lever's not working!

Orange: What do you mean-

Sabre: I got it!

(Sabre runs over and absorbs the energy from the generator.)

Yellow: ...What the-

Orange: Don't question it, for now just run.

—

(Dark and Orange fighting. Dark misses a fireball, and it heads straight for Sabre.)

Orange: SABRE, LOOK OUT!

(Sabre turns around, catches the fireball, and absorbs it.)

Dark: Wait- what?!

Orange: NICE!

(Orange punches Dark in the face.)

—

(Orange is now Rainbow. Reverse is being a problem, does the thing where he tries to destroy Sabre, but Rainbow is unable to intervene here. Reverse fires the thing, but Sabre just catches it and absorbs it.)

Reverse: ...What.

Sabre: You messed with the wrong guy.

—

(Nightmare has taken the Orange Village to his lair, and Sabre is coming to save them. However, instead of being stealthy... Sabre just starts absorbing all of the Darkness beings as soon as he gets there. Nightmare is panicking.)

Nightmare: (Being contacted through a speaker system) What is it now?!

(Dark heard panicking through the speaker)

Nightmare: (Getting up and running to the door) WHAT DO YOU MEAN HE'S ABSORBING ALL OF THEM?! THERE'S ALMOST A HUNDRED DARKNESS OUT THERE! HOW IS HE EVEN HERE?!

(Nightmare runs out, leaving the captured Orange Steves alone.)

Happy: He's gotta be talking about Sabre!

Shy: H-how is he even able to absorb all those things?

Funny: My theory is he's a living black hole.

Orange Leader: Are you all ignoring the fact that there's a hundred Darkness out there and Sabre is absorbing ALL OF THEM?

(Sabre runs in to get them out, and can actually take them through the facility and not escape through the sewers. Because sure enough, all the Darkness is gone.)

Orange: Hey uh, question; Where did all the Darkness go?

Sabre: Ehhh don't worry about it.

—

Okay, enough funny situations. Now here's some slight drama:

Since Sabre is constantly looking for things to absorb, he doesn't care what it is as long as he's able/allowed to absorb it. However, he's often up at night searching the area he's in for things to absorb because of this. He knows to search outside the area of where his friends are, so he doesn't accidentally absorb something precious to them.

This means that he often goes into forests and abandoned places at night, looking for things he can absorb. Naturally, a bunch of wildlife goes missing, and it's not uncommon for groups of Darkness scouts to go missing either. Everyone is a little worried when this happens, as they don't know how there can be something a bigger threat than the Darkness, and it's creepy that a bunch of random woodland animals suddenly disappear. Around when just before the Sol arc happens, groups of Colorless Guards look for the mysterious thing in the woods. Sabre is sneaky though, and never gets caught.

This, of course, doesn't really help with the whole "panic about the mysterious threat" thing.

Another thing is, when Sabre absorbs Darkness their corruption makes him lose it a tiny bit, making him search for things to absorb the same way the Darkness looks for things to corrupt. This is what causes Sabre to start going out at night to absorb random things, which happens often, as when the Steves found out he can absorb Darkness no problem they send him out to get rid of it in places a lot. Sabre kept doing that after the Darkness was gone, though, as he found use in absorbing things in secret; nobody would be there to see what things he absorbed, and he was able to keep himself from absorbing random things during the day... most of the time.

I see many opportunities for angst in this AU :)