Puzzles.

Holy shit there were puzzles!

Mettaton stared at the second switch and rolled his eyes, flicking it with such ease and grace that it appeared simple enough for a child to do.

Oh wait, it was simple enough for a child to do!

"Y'know," he said, turning around once the task was complete. "I don't think it's an overly difficult puzzle when you mark which switch is supposed to be flipped."

Chara blushed- more than usual- and swiveled their eyes to the side slightly, arms folding. "Yeah, well, I'm used to kids coming down here, okay? Jeez. You're the oldest one I've seen since…"

The teen paused. Their red, hardened eyes glazed over with a look of longing. Mettaton didn't recognize it at first, but it didn't take long for the emotion to click with him. It was what he felt when all of his cousins went missing. That feeling of want, need...loneliness...emptiness.

"Are you alright, darling?" he asked. The robot's head moved forward slightly while his mind whizzed around in trying to process all the nonverbal cues Chara had been giving off. He was about to open his mouth once more when the living human moved a hand in front of him, blinking away any signs of distraught that they had previously been experiencing.

"I'm fine," they replied quickly, regaining the confident composure held before.

Mettaton blinked, his face moving back away from the hand but expression of curiosity still remaining. "Since when?"

"Since nothing." Chara turned sharply toward the room's exit and began to make their way out when a hand reached for them. It lightly graced their shoulder, making them pause, before retracting back to its owner, who now held not a look of curiosity, but a soft expression.

"Darling, if something's bothering you, it's not good to keep it bottled up like that."

"Don't call me darling," was all Chara said before leading the robot into the next room.

It wasn't until they had reached the next area that the tension was broken by words, which, of course, were spoken by the more experienced of the two on the Underground. It was preceded by a small sigh, but eventually, words did come out.

"Things are probably gonna attack you down here. Look, it's...they're not that harmful, okay? I don't know how many times I have to say this…" They sighed once more (though more of a 'huff' this time) and made their way over to the training dummy, giving it a small pat on the head. "Just take this dummy for example. Is it gonna kill you? No! So don't fucking attack it. Monsters will jump out and-"

"Woah woah woah!" Mettaton's vibrant magenta eyes widened as he took a small step back. "Monsters? You mean like that fish thing?"

"Uh, kinda. Not really-"

"Things are gonna try to kill me!?"

This is the part where Chara would let out a breath of aggravation, their hand running against their face to calm themself. "No, no... NO! Look, the monsters in the Ruins just get spooked a little easily, okay? No one's gonna hurt you! DO NOT. FUCKING. FIGHT ANYONE."

The robot, mouth open to speak, quickly closed it, deciding against saying anything back. The look in Chara's red eyes was enough to convince him of that. Right. No fighting. Got it.

After a moment to ensure no retaliations would occur, Chara patted the dummy on the head again lightly, sighed, then pointed toward Mettaton's heart, which began to seep back out of his chest and into the open air. Three buttons sprawled out beneath him- ACT, ITEM, and MERCY- which his own set of magenta eyes immediately drew toward.

"If something attacks you, just wait. Like I said, the monsters here aren't very strong or powerful. They can't kill you. They're just a little frightened. If you talk to them for long enough, I can come over and calm 'em down, 'kay? It's not too hard. Don't make any sudden movements and you should be good." It was at that point Chara nudged their head toward the dummy, taking a small step back and shooting the robot a smile. "Try practicing on this guy."

Mettaton nodded before once more redirecting his eyes on the buttons below him. FIGHT, ACT, ITE-...wait, there were four buttons now. When did the fourth one get there?

"Hehehe..."

Mettaton's head whipped around, but when he scanned the room for signs of life, he found it was just him and Chara. Well, that he could see, anyway. There might be an invisible monster or something… He really didn't want to think about that possibility.

"Did you hear that?" was all he asked, to which Chara raised an eyebrow.

"Hear what?"

The robot paused for a moment, waiting to hear any other audible noises, but simply shook his head.

"It was probably just a froggit," Chara muttered before taking another step back. "Well?"

"Oh, right, sorry."

It was at this point Mettaton blinked, a wide smile spreading across his face, and he strode forward.

*Y-you encounter the Dummy.

Mettaton's head whipped around once more, but just like last time, there was no face to put the voice to. Only Chara's confused one, and he was pretty sure it sounded a lot more girly than theirs.

He simply let out a small sigh, moving his hand out to the various different buttons and watching as the heart followed each. Hey, Chara said not to FIGHT, so...ACT?

*D-Dummy

Right. Yup. This was the Dummy.

*Check or...t-talk?

Okay, now he's pretty sure there's either someone there or he's going crazy, but it's probably best not to look like you've lost your marbles, right? Yeah. Chara obviously can't hear that voice, so just pretend it's not there…

Slowly, Mettaton moved his hand over to the 'Check' button, allowing it to stay there for a moment before he turned his attention toward the dummy.

*Dummy - Attack z-zero, defense z-zero

*C-cotton heart and cyan SOUL…

*He rem-minds you of someone.

"He does?" Mettaton blinked, watching as the dummy remained unmoving and leaving his heart on the 'check' option.

*Dummy st-stands around absentmindedly.

Yeah...he can see that. You don't have to narrate everything, disembodied voice.

The former human tilted his head slightly, eyes gracing the figure's form. Well, he certainly hadn't seen the dummy before, but...the voice was right. It did remind him of someone. But...who?

*D-Dummy looks like it's going t-to fall over.

Mettaton's eyes widened as he continued staring. Well, if it fell over, then he'd just have to pick it back up! After all, wouldn't want this place to look like a garbage can, would we?

*...

"..."

At least the voice stopped. That was a relief.

*...I-it's a dummy…

Never mind.

Mettaton continued watching the dummy, ignoring the voice's remark about why it wasn't replying. He didn't expect it to reply. He expected to find out why the thing was reminding him of someone. Instead, he got to watch the thing casually...float away? Okay, that's...probably not the weirdest thing so far (it's still a tie between being a robot and Fishy the Fish). Definitely up there, though.

*D-Dummy tires of your aimless shen-nanigans…

It does? Mettaton turned his head back to where he was certain he heard the voice but shook it once more upon finding nothing. Okay, definitely going crazy. A lot of definites for someone so confused as to what was going on.

*You w-won!

*You earned z-zero XP and zero g-gold.

Chara, who, mind you, had been watching the entire scene, could only stare at the dummy with an expression just as baffled as the robot's. They blinked a few times at where the dummy had originally stood and simply shook their head, turning to leave.

"C'mon," they said before exiting into the next room.

Mettaton, however did not follow at first. He took another look around the room after watching Chara make their way through the exit, eyes scanning for another creature and, finally, gasping, jumping a full yard back when he saw one.

What caused the robot distress was not anything particularly intimidating, but instead, a small yellow lizard-looking creature stood in the middle of the room, a smile perched on her face as she cheerfully raised a mustard-colored hand to wave.

"H-hi," the creature said, rubbing her hands along her white T-shirt, clicking a pen in the chest pocket before nodding towards the astonished metallic creature.

Said man blinked, slowly gaining the confidence to reach his hand out toward the lizard girl, who chuckled nervously. When his hand went through her, however, she simply laughed even more.

"You can't t-touch me," she said, arms folding across her chest, specifically the area his metallic hand had reached through. "I-I'm a ghost."

"Were you the one talking?" the robot asked, taking a quick peek at where the dummy had been before quickly refocusing his gaze on the being in front of him, who nodded.

"Yeah, that was...th-that was me. I, uh, I thought you might need some…" Her eyes darted to the side. "...help?"

"Why do you sound so unsure, darling?" Mettaton asked, adding in a quick chuckle of his own. If she really was a ghost (and, contrary to what he might have believed before he died, there certainly seemed to be a life after death...or he was dreaming. Or going crazy. All three seemed pretty likely, to think of it…), she certainly was a nice one. It seemed like it, anyway. "It was nice of you to try helping me. I thank you for that!"

The ghost blinked a few times, eyes wide, a small blush crossing over her face. "You...y-you do?"

"Of course," he added in, offering her a warm smile in return. "You remind me a lot of my cousin, you know."

"I do? O-oh, uh…" The ghost was still trying to think of a way to finish that, however, when the sight of the human from earlier caught her eye, and she quickly side-stepped out of Mettaton's view. "I-I think you should go now."

"What's taking so long?"

Mettaton turned his head at the sound of the voice, giving a small smile to his current companion as well when they caught his sight. "I was just talking to, uh…" Oh, that's right! He hadn't gotten her name yet. "...lovely…"

However, when he turned back to the spot he could have sworn she was in, there was nothing visible but air, causing Mettaton's face to scrunch in confusion and Chara to raise an eyebrow.

"I swear," he repeated, now redirecting his attention to the human in front of him. "There was someone there. I know there was."

Chara nodded, turned around and waved for him to follow. Riiiight...someone there. Of course. They simply shrugged before heading to the next room over, this time barely giving Mettaton much of a chance to catch up. Thankfully, he was fast.

Once he had managed to reach the living teen, Mettaton took a glance beyond them and frowned. Man, this place was so bleak…

"There's another puzzle here, I think," the living teen said as they took a couple steps ahead. "Hope you know how to solve it."

The two began to make their way forward when, suddenly, a large frog-like creature stepped onto the path. Well, large for a frog. It only stood up a little past Mettaton's calf, but for a frog, it might has well been on steroids.

*F-Froggit attacks you, the dinosaur lady from earlier muttered, causing Mettaton to take another glimpse around. It seemed as if Chara hadn't noticed the intrusion and continued forward, much to the robot's dismay.

Once more, when the heart popped out of his chest, he let it hover over the 'ACT' then 'Check' options and observed the creature.

*Froggit - Attack four, defense f-five

*Life is d-difficult for…for…

Mettaton blinked once, taking a quick glance back to where he could have sworn the voice was coming from. That ghost from earlier...she sounded almost...afraid?

"Darling?" Mettaton called out, causing Chara to turn their head. Oh, geez, a monster. Let's ignore the fact that Mettaton is looking the wrong way. Instead, they quickly skipped over toward the monster and gently picked it up, giving a half-hearted smile to the thing in the process.

"Hey, lil' guy. You got lost, huh?"

This, in turn, made Mettaton look back at his current guide, who was now cradling the froggit like a little baby. Honestly, if it was anyone else, they probably would have laughed at the sudden change from rugged tomboy to caring mother in a matter of seconds, but this was not anyone. This was Mettaton, and he would only watch with intrigue. Wow...there's a side of them he'd never thought he'd see (granted they haven't been together any longer than fifteen minutes, but a lot has happened in that fifteen minutes).

"There you go," the human said, bending down to allow the froggit to slide out of their arms. "And go tell your friends that he won't hurt them either."

After watching the monster calmly hop away, Chara then turned back to the robot. There was a peaceful expression present on their face, though this was quickly replaced when their attention had been caught by said bot's stare.

"What?" they hissed, body language reverting to the default assertive toughness.

"Nothing," Mettaton replied, and, honestly, his even tone implied that he did, in fact, have nothing against what had just occurred, which was...surprising. The teen was at least expecting a bit of a bitten down snicker or something, but those magenta eyes...they only showed understanding. It was certainly not something Chara was used to from a human soul.

They probably should have said something- they really should've said something- but Chara was feeling just the slightest bit off put by the lack of this human's normality. Honestly, that was something they should be grateful for. Humans were horrible creatures... No, instead, they turned their eyes sharply to the side before continuing on.

It wasn't until the pair had reached a small bridge that the alive one looked back at their dead companion. Mettaton had caught a glimpse of a sign they passed and thought he felt something drawing him to it, but all it said was something about blueprints (and not his), so he decided to ignore it.

"This is the puzzle…" Chara muttered once they had reached a bridge coated in spikes. Mettaton took one glance at the puzzle and flinched away.

"How am I supposed to get over that!?"

"Yeah... " They sighed, eyes meandering over it once more. Honesty, they weren't entirely sure what they were thinking when they had first created that thing… It was their first puzzle, after all. That...probably explained a lot. "Here just, uh...follow me."

The human trailed their foot along the edge of the puzzle for a moment before taking a firm step along one of the spike edges, which then receded away from their feet. Honestly, they'd memorized most (if not, all) the puzzles in the Ruins, but they still understood why some seemed intimidating to others.

The robot, on the other hand, would quickly shake his head. "What if I miss step? What if I fall into the water? Can this body even handle water!?"

"Fine," Chara groaned and reached back to grab a firm hold of Mettaton's hand. They really didn't feel like putting up with this today. "Try not to slip."

It took but a matter of a minute or two before the two made it across, at which point the more masculine one (yes, the still-living one) would mutter something along the lines of, "I have no idea what the hell was running through my mind…" before letting go of Mettaton's hand and hurrying through to the next room, the robot keeping right at their heels.

Though, upon entering a long hallway, Chara snapped their fingers and hastily shouted out, "SHIT!"

"What is it?"

They clapped their hands together suddenly, staring at Mettaton with wide eyes and a tight frown, then quickly spun around in the opposite direction. "Look, I gotta grab a few things from the store," they said, already speed walking down the hall. "You did fine so far, so I don't think you should have much trouble up ahead."

The robot nodded, doing his best to keep up with the living human as they hurried forward.

"Just remember what I said- talk to the monsters and calm 'em down. You should be fine. My house is at the end of the Ruins and the puzzles between here and there aren't too difficult, so just meet me down there, 'kay?"

Once at the end of the hall, Chara turned back to their companion for an answer, to which he nodded.

"Cool."

And just like that, they were gone.

Wow, I have people making suggestions already after the first chapter. I...should probably explain what this AU is about, huh?

Alright, uh, before we delve into that, I wanna answer some comments...well, one comment from chapter one, though hopefully more in the future.

MIGHTYNO.9SUCKS - I appreciate the fact that you like this enough to make suggestions! There will be some more about those below, but just to let you know, two of your suggestions I had already planned on doing, so...stop predicting the future!

Now, uh, what this AU is about... It started out just taking a list of characters and putting them through an algorithm which used both StoryShift and UnderSwap roles. If EquationTale seems like a rip off of either of those...sorry? Uh, it's more than just characters in weird roles, though, so hopefully the story is different enough from them that it doesn't seem like that...

To those who don't know what an algorithm is, using the definition by Google, "a process or set of rules to be followed in calculations or other problem-solving operations, especially by a computer." I'm essentially creating an equation and plugging in characters. In short: math. I'm using math to find out what character goes where. Hence the name, EquationTale. The only one that doesn't follow this rule is the person in Papyrus's role, but that's because I'm having trouble finding a reason as to why one of Muffet's spider babies would replace the Great Papyrus...

If we're talking story-wise and want to break the fourth wall, then whoever is playing this version of UnderTale tried to corrupt the game by messing with the game's coding, however only ended up changing what people are where.

The point still remains, though, that I already have all the characters assigned roles. After all, the whole point of this was to take weird, freaky shifts (like Chara being in Toriel's spot, Mettaton being in Frisk's spot, etc.) and trying to come up with a story that makes sense. If I happen to have missed some minor characters and need suggestions for them, then I will ask, but for the most part, everyone already has their role.

I appreciate you guys liking the story enough for suggestions, though! It just makes me more DETERMINED!

Also, uh, the more people that like my story and follow it, the more motivation I have to continue...so don't be afraid to share this fanfic with others! I have a tendency to loose motivation for stories easily...it would help immensely!