A/N: I've edited this chapter slightly to fit in with some world-building. If you've read it before, however, you don't need to reread it (unless you want to, of course).

This idea for the Undertale songs to be living, sentient beings randomly came to me and wouldn't go away, so I decided to write it as a silly little thing... My hand slipped. Enjoy some feels instead.
As for a SPOILER WARNING, there are major spoilers for the genocide route in this chapter, and future chapters will contain spoilers for the entire game.
Also, I just want to say right now that Sans' speech will have normal capitalization. Sorry, it's just very highly annoying for me to try to write a story with any length to it with Sans' all-lowercase style. I managed for one of my other Undertale stories, but for this one, I decided to just use normal capitalization.


Chapter 1: Megalovania

It's not very well-known that within the Underground, spirits known as Themes live. Each Theme binds itself to a person or a place to gain power, and, in return, it lends its power to the person or protection to the place. Themes don't provide much direct power on their own, but they can take the power provided to them from the person or place, their Bonded, and increase it. On top of this, each Theme produces a unique song for its person or place that it binds itself to, and some of the more powerful Themes have two or three songs as part of their power. Once a Theme binds itself to a person or place, the link is permanent, and if that person dies or the place is destroyed, the Theme's power will greatly decrease, or it may die altogether. To avoid this, some Themes bind themselves to the world at large, or to a situation, but this is rare because a Theme that does this gets used very often without gaining much power in return, and it can be rather tiring.

Among the Themes was one particularly bold and impressive spirit named Megalovania. Megalovania, who usually just went by Mega for short, had six melodies, which was an impressively high number, though not as much as what some other Themes had. One was a fun song that Mega could display without even trying. It didn't require any power transfer, and Mega figured that it would serve whoever Mega eventually bonded to well. Another was a more calm and mysterious melody that also really didn't require any power, though it could channel a little bit of non-combative magic. A third was a more gentle and calm, yet upbeat melody that was actually a variation on the first. The fourth was also a variation on the first... sort of. It was a combative melody, and it channeled about the same amount of magic energy as most Themes' combative melodies. The fifth was a very slow, calm, and almost emotional song. All of these, however, paled in comparison to the last one, the sixth melody. It was a song full of power, one that could take and channel extremely high levels of magic easily. It was the most powerful melody in terms of raw magic channeling capabilities of any Theme. Megalovania knew that this melody, its "title melody," if you would, was very magnificent and powerful, so it hesitated to bind itself to anyone or any place. It decided that it didn't want to be bound to a place, but that left it with finding a worthy person.

The problem was that Mega was the type of Theme that knew that it was incredible, and it also knew just how exhausting that type of power was. If it was going to display its music and power, it was going to do it right, and if it was going to do it right, it was certainly not going to do it often. Mega wanted someone who had a lot of power so that whoever it was could fuel Mega, but that person needed to not get into battles very often. Besides, Mega had an ego. It only wanted to be used in battle if that battle was righteous.

Other Themes had discussed the matter of a young skeleton named Sans. The guy had a lot of raw power, and he would be any Theme's dream to bond with except for one thing: he never fought. The guy laughed and joked his way out of everything. Sure, he practiced like crazy, but Themes bound to people only gained power from those people's actual fights, not practices. Of course, some Themes had melodies that didn't require a power transfer, such as Mega's first, fun melody, but Theme gained little to no benefit from using these. Of course, a Theme could practice its music and practice using power with its Bonded at any time, but it still wouldn't get any real power or any benefits from mere practices.

Bonetrousle, another Theme, had noticed Sans, but decided to favor his younger brother, Papyrus. A while after Bonetrousle and Papyrus had bonded, Bonetrousle decided to talk to Megalovania, since the two Themes were friends. After the usual pleasantries, Bonetrousle said, "Mega, you've heard about this Sans guy, right?"

"Well, of course I've heard about him. Why do you ask?"

"You know how everyone puts him down because the guy won't fight, right? But today, someone decided to mess with my Bonded, Papyrus, and I swear that guy Sans looked so very threatening. He started to initiate a fight, which is enough to trigger a Theme, you know, and one of his eyes was glowing blue. The person who was messing with Papyrus just left."

"What's your point, exactly?"

"Sans isn't unwilling to fight, like most Themes think he is. He's just not going to fight unless he has a very good reason to."

Megalovania thought about this long and hard. Sans sounded like the perfect Bonded to Mega, actually. After all, it did want someone who wouldn't fight much, and who would only fight for a very good reason. "You're saying that you think that Sans would be a good candidate for being my Bonded?" Mega clarified.

Bonetrousle nodded. "That's exactly what I'm saying. Besides, we're friends, right? We would get to see each other all the time!"

Mega laughed a little. "I guess we're good enough friends that I suppose that I could put up with constantly being near you…" it said teasingly.

"Come on! I have a less combative melody, and you have a couple non-combative melodies, and you know that our least powerful ones go well together! We could use our relaxed melodies together all the time!"

Laughing more, Mega said, "They really don't go together. You're just desperate to be around me."

"I am not desperate! I don't even really want you around. I just thought that Sans sounded like a good fit for you," Bonetrousle said, trying and failing to look aloof.

"Uh huh…" Mega said disbelievingly. It relented, however, and it smiled before adding, "I'll look into the guy."

"You should! Go check him out and then come talk to me!" Bonetrousle exclaimed.

Megalovania invisibly made its way over to Snowdin, where the skeleton brothers had recently moved to. It decided to watch Sans for a while… and it found itself bored but intrigued. Sure, Sans didn't do anything, but he was always watching. The guy was more calculating than anyone gave him credit for.

Uncertain, Mega watched Sans for three whole days as Sans went about his normal business: looking out for his brother, napping, going to Grillby's, checking up on his brother, fiddling with the machine kept in the back room of his house, making notes about timelines, practicing his magic, and keeping an eye on his brother. All the while, Sans seemed easygoing and relaxed, but invisible Megalovania noticed Sans' keen stare as he carefully watched out for any potential dangers.

Finally, on the fourth day of watching Sans, he saw something interesting. Sans and Papyrus were going out on a picnic because Papyrus had insisted that they do so. Sans was reluctant, but he didn't want to say no to his brother. As the two sat and ate, another monster came up to them.

"So, you're the new freaks in town, huh?" the monster said with a sneer.

"Yup," Sans replied, "spooky, freaky skeletons right here."

"Hah, you two should get out of town! Snowdin isn't meant for creepy weirdos like you!" The monster tried to shove Sans, but Sans dodged with unnatural speed. The other monster laughed. "What, you can't take a hit?"

Papyrus was getting mad, and Megalovania saw Bonetrousle become visible as Papyrus prepped to fight. "LEAVE MY BROTHER ALONE! HE DOESN'T HAVE MUCH HP, ALRIGHT? YOU SHOULD NOT GIVE HIM A HARD TIME ABOUT IT!"

"So he's a wimp, huh?"

"What can I say? With 1 HP, I guess I'm more fragile than ivory. You'd think I'd be bone-hard, but nope. It's a real irony," Sans commented with a shrug.

The other monster scoffed at Sans' puns. "So if you two are that weak, you should get out of town before someone gets the idea to kill you, don't you think?" He accentuated this with a hard shove at Papyrus, which knocked 1 HP off of Papyrus' overall health.

"Now, who would want to do that?" Sans asked. His tone was perfectly normal, but his white pupils vanished, leaving his eyes black and menacing.

"I'm not scared of you! You're a weakling!" the other monster spat.

The other monster's HP dropped very quickly as Sans used blue magic to smash him into the ground and summoned bone attacks to cut his HP down further. "I'm sorry, what did you say?" Sans asked.

The other monster didn't reply as he charged at Sans, but Sans sidestepped with ease, allowing the monster to run right past him. "UGH, just stand there and take it!" the other monster growled.

"Eh, nope. Sorry, I'm not suicidal," Sans said, summoning more attacks that now involved Gaster Blasters. The other monster's HP dropped below half.

Megalovania noticed the Snowdin Theme supporting Sans with its out-of-borders melody, which it called "Snowy" and saw how much strength it was getting from Sans' righteous defense of his brother.

In that moment, Megalovania decided to bond with Sans.

It was a very sudden thing. Right after Sans dodged another one of the other monster's attacks, Megalovania appeared to him. "I've taken a liking to you," it said quickly. "I've been watching you, and you don't fight unless you have a darn good reason. You're exactly what I want. Do you want to bond with me?"

Sans didn't immediately reply as he dodged again. He knew that being chosen by a Theme was a great honor, however, so he didn't take long to think about it. "Sure, I'll do it," he said, keeping his eye on his enemy even as he held his hand out to Megalovania.

The Theme took the skeleton's hand, sealing the bond. It then repositioned itself right behind Sans and synched itself up with the skeleton's soul. As it felt Sans' power rushing through it, it began to display its unique music. Sans froze for a second, looking behind him at the Theme in disbelief as it shrugged modestly. "What can I say? I am very great, and I required someone just as great to be my Bonded."

Sans shook his head in disbelief before he turned forward to face the now very intimidated foe. "Well, it seems that I just got a Theme, and I'd really love to try it out. Do you want be my practice dummy?" he asked innocently, but a flash of blue in his eye assured the other monster that this 'practice' would not be innocent.

The other monster, however, had taken the chance while Sans was talking to Mega to heal, so his health was full, temporarily assuaging any fears of Sans and of the powers of Themes. The monster yelled in fury and exclaimed, "So what if you got a Theme?! I don't care! I want you gone! You're-you're as bad as that creepy Gaster guy!"

All humor drained from Sans' face. "What did you say, buddy?"

The poor monster never had a chance to reply as the newly strengthened Sans came at him full-force, not relenting as he displayed attack after attack after attack.

Megalovania loved every second of it. "I will never regret choosing this guy. Even if this is the only time we ever fight, this rush of power and righteous anger is worth it!"

It was over all too soon as the other monster's HP dropped to 1 and Sans stopped. "Now then, are we done here?" he asked.

"Y… Y… You're a FREAK, ya hear me?! You'll NEVER be accepted ANYWHERE in the Underground! I don't care if you have a Theme, you'll never survive with 1 HP! That Theme is the stupidest Theme ever to bind itself to such a weak monster! You'll die, and you'll either kill that Theme or severely weaken it, and a Theme that great shouldn't be wasted on you!"

Sans waited for the other monster to finish his rant. "Are we done here?" he repeated calmly.

Sputtering, the other monster hobbled away.

"That was incredible," Megalovania panted a little as it looked down at Sans from where it was floating. "You're incredible."

"I hate to break it to you, but I don't normally do that," Sans said.

"I know that. That's why I chose you. I'm not a junkie for fights like some other Themes. I only want to be called upon when it's necessary, and you seem like just the right guy for that. Besides, I have six melodies, and I think that the most relaxed one fits you." Mega started showing off its fun, easy-going melody.

Sans smiled at the Theme as he nodded in time to the fun beat of Mega's tune. "That's great," he said. "What's your name, then?"

"I'm Megalovania, but you can call me Mega. Your brother's theme, Bonetrousle, is a friend of mine."

"Nice to meet you, Mega. It'll be great big fun to work with you. We'll have a mega-good time."

Megalovania laughed, and both the skeleton and the Theme knew that they had found a kindred spirit.


"I'm sorry, Mega. I know you don't want to fight, but…"

"Sans, I never said that I didn't want to fight. I'm a Theme for crying out loud. I live off of fights. I only said that I didn't want to fight for no reason. This counts as a good reason."

"Alright then… I don't want to fight."

"Try to convince the kiddo to RESET, then, but you and I both know that something has to be done to stop that human."

Sans bowed his head. "I know. This kid though… this human has a lot of LV by now, so this battle just might take me down. I'll do my best, but…"

"I'm here with you, Sans. Either we'll save the world together by sending this creature back to hell where it belongs, or we'll die trying."

"Thanks for everything, Mega."

"I wouldn't change it if I could."

They both knew how much that meant to Sans. Megalovania couldn't retain memory after the RESETs, but it knew about Sans' memories. It knew that Sans had watched various versions of the world, though this was the first time that the human had decided to literally slaughter everything. Sans had mostly just let things run their course since it would all RESET anyway, but he'd calculated that if the kid finished what had been started this time around, there might not be a RESET. So, reluctantly, both Mega and Sans decided to fight.

The kid appeared at the end of a corridor. The time had come. Megalovania looked out the widows at the barrier-tinted light with tears in its eyes. This was the end of it all, one way or another. Sans' resolve, however, didn't waver. "It's a beautiful day outside. Birds are singing. Flowers are blooming. On days like these, kids like you…" Megalovania felt the rush of power as the battle started and Sans declared, "…SHOULD BE BURNING IN HELL."

The attacks started full force, and Megalovania started up. It had never felt more alive, and it knew that it had never performed better. It focused all of its energy, including the energy that it was receiving from the fight, into strengthening Sans and distracting the human. The battle was fierce and draining, but Mega and Sans couldn't give up.

Megalovania suddenly froze as Sans stopped the fight, trying to spare the kid. The human didn't even pause before striking at Sans again, and Mega struck back into action. Even giving his all, he could tell that Sans' energy was being seriously depleted by all of the attacks. Sans had joked at the beginning of the fight about not knowing why people didn't start with their strongest attack, but Mega and Sans both knew well why that was. The strongest attacks of those with Themes were usually saved for the end when the Theme had built up enough energy to support the attack and get its Bonded through the intense struggle of using more magic than what the monster was used to. Sans, however, completely ignored this as he started out too strong, which forced him to back off a little to save his magic as Mega built up power.

Sans and Mega were linked closely enough to know that Sans' overall magic reserves were running low, and while a Theme could make a little magic go a long way, it couldn't replenish magic that simply wasn't there anymore. They also both knew that Mega was pretty well ready to initiate Sans' most powerful attacks and to pull him through it. "Well, here goes nothing…" Sans told the kid. "Are you ready? Survive THIS, and I'll show you my special attack!"

Megalovania focused all of its energy into Sans as he focused all of his magic into the attacks at hand. There was no special attack coming; this was the moment of truth. Either they would kill the kid now, or they would have to hope that Sans' plan B of boring the kid to death would work. Honestly, neither really thought that it would, but it was still worth trying if this one last display of their combined power didn't work. Mega focused harder than it ever had in its life. It felt victorious as their combined power threw attack after attack at the abomination in front of them. They were doing so well! And yet…

Sans' magic ran out. Megalovania felt beyond crushed as Sans was forced to resort to the desperate 'special attack' of doing nothing. It knew it had failed, and Sans' plan B probably wouldn't work. Mega rested its head in its hand as their fate was left to Sans alone. It didn't escape its notice that Sans knew the fight's barrier's weak spot and was using the last of his magic to keep the kid's SOUL away from that weak point. Mega rested a hand on Sans' shoulder to support him as he stayed awake despite his exhaustion to keep teleporting the kid's SOUL. Eventually, however, the kid gave up, and Sans and Mega were both so tired…

SLASH! The kid struck at Sans. Thankfully, Sans had had the presence of mind to still be able to dodge, but he wasn't expecting the second slash.

"SANS, NO!" Mega yelled. "Sans, I'm so, so sorry! If I was better at my job…"

"Mega," Sans whispered quietly, "you're perfect. I couldn't have asked for a better partner. I wouldn't change being with you even if I could." Sans then looked over at the kid, defeated. "So… guess that's it, huh? Just… don't say I didn't warn you." Sans then stood up wearily and started walking off. "Welp, I'm going to Grillby's," he announced.

"I'm coming with you," Megalovania said with a sad smile as it felt its life force draining. "We'll see Bonetrousle and Papyrus there, right? I think old Bone will want some fries. What about Pap?"

"Let me ask," Sans said, returning his Theme's sad smile. More loudly, he asked, "Papyrus, do you want anything?"

Megalovania could only watch as Sans dissolved into ash. Mega shed a few tears as it felt its Bonded slip away, taking its life-force with him. "I'm right behind you," it muttered as it, too, dissolved into nothing.


A/N: Did you like the feels?
Just in case it wasn't clear to everyone, the six songs that Megalovania has are sans., Premonition, It's Raining Somewhere Else, Song That Might Play When You Fight Sans, The Choice, and, of course, Megalovania. Bonetrousle's alternate melody is Nyeh Heh Heh!, and the Snowdin Theme's song that was playing at the beginning of Sans' first fight was Snowy.
Please let me know what you think! I am open to suggestions for future songs. Chapter 2 is going to be Spear of Justice and the other songs having to do with Undyne, but if you have suggestions for songs beyond that, I would love to hear them! It doesn't matter where in the timeline they would have to fall, as my next chapter will take place chronologically before this one.
Just as a note, I am making no promises for my posting schedule. I could take up to a couple months per chapter due to my busy life and the fact that I'm also working on other stories.