Batman did not kill. That didn't mean he was a stranger to violence and death. He'd seen death before. It all started with death, after all.
Batman did not kill. He fought, and he couldn't save everyone. He knew that.
Batman did not kill.
Perhaps back when he was less experienced, less knowledgeable, younger, more reckless, less controlled... Before he put on the mask, before he became Batman... There were times vigilante justice wound up with more than broken bones. Crossfire. Self defense. Honest mistakes. He did his best, but back then, his best wasn't enough. And he wept for it, knowing he had to improve, lest others were killed in his wake.
Superstitious and cowardly as they were, criminals were still people. People with families, friends. Perhaps they were driven by circumstance. Perhaps they were driven by greed. But people nonetheless.
Batman believed he couldn't protect the streets by killing those who walked it. Restorative and correctional justice wasn't useless. Wayne Industries hired people on parole, never turning someone away simply because they had a record. More often than not, it'd stop them from turning back to crime. He knew the statistics. Unemployment and crime, especially among those who'd committed before, went hand-in-hand. Nobody deserved to be defined by their worst mistakes. He of all people knew that.
His enemy was crime, not those who committed it. A battle fought from both sides, as Batman and Bruce Wayne.
A battle in which he would never kill.
Undyne wasn't his adversary in that battle.
She tried to kill him, but not for her own gain.
She risked her life to take his soul and free her people. Her family, her friends.
Giving his soul up to her wasn't an option, but to kill her...
He refused to kill even the lowliest of villains, yet here, he'd turned a hero into dust.
Why? Why did this happen? How?
Nothing he hit her with should have been enough to kill her, even when taking physiological differences that would arise from her being piscine and possibly amphibious into account. She was meant to be knocked unconscious as quickly as possible, yet she wasn't knocked out despite failing to dodge any of his attacks. Given some thought, her entire death left many questions to answer. She melted, then turned into dust. Was this also due to magic?
It was possible that her armor concealed some level of bruising, but being hit numerous times did nothing to hinder her, nor was her armor visibly dented or damaged in any way. Most people would have slowed from and shown signs of pain within seconds. She didn't bruise or bleed. In fact, until she began to turn to dust, she seemed completely untouched throughout the entire battle.
He'd examine her corpse, analyzing it and studying it for some clue, some explanation as to how this happened, how she worked, but he couldn't.
She was dust, scattered throughout Waterfall. He couldn't even take a sample - no test tube or bag to contain it, no microscope with which to analyze it, no computer to scan it.
Not even her armor remained, hence it was either part of her body or magic as well.
He couldn't let that happen again.
There wasn't anything he could reasonably do about her death. What was done was done. It wasn't as if he had any way to go back in time. He'd bear the guilt of murdering her for as long as he lived. That wouldn't change. But there were things he could change.
He'd been working under the assumption that the biology of the monsters he'd encounter would be at least somewhat analogous to those of other lifeforms he'd already encountered, terrestrial, alien, or otherwise. Now he had proof that things that he'd believed were universal regarding biology were not. The way injuries worked, respiration, nervous systems... Even whether or not beings that lived down here even had cells had been thrown into question.
He didn't know whether or not all monsters became dust when they died, or whether different species of monsters would operate differently in that manner. Come to think of it, he hadn't seen any medical facilities nearby. Did they not have them? Was Snowdin not populated enough for one? Or were there cultural, socioeconomic, or biological differences in the fundamental treatment and perception of health and healthcare?
Batman was beginning to realize just how out of his depth he was in this subterranean world of magic and monsters.
He knew Flowey was still following him, and expected the flower to make its presence known and gloat at him. It did seem intent on the idea of him killing someone not so long ago. But the flower didn't show itself or laugh at him. Whatever it wanted, whatever it expected from him, it wasn't done yet. Could the flower have been right? Was this strange world really one where he must kill or be killed?
No. There was always another way. No matter how difficult, he would find it. He couldn't consider any alternatives. He would not kill.
The first order of business would then be to relearn everything. The flower knew he wasn't from "this world" and how it worked, but wouldn't likely be willing to answer his questions. Humans did exist somewhere on the surface, but that wasn't currently accessible. He could speak to Toriel. He wasn't certain of how much she knew or how honest she would be, but she'd be an available source of information. Grillby was also a possibility. He'd have to pay the library a visit as well.
Or, as the sign called it, the "LIBRARBY." The institution hadn't given him a good impression when he first walked past it, and it wasn't giving him a good impression now.
He stepped in. The monster at the counter greeted him.
"Welcome to Snowdin Library. Yes, we know the sign's misspelled."
Batman gave the green lizard a nod in acknowledgement, then took a look around and was struck by the impulse to add the library to the list of Wayne Foundation charitable funding projects. The state of the library was dismal.
Six shelves with net total of roughly a hundred books were arranged by colour and lined against the back wall. A singular squat table with no chairs. It wasn't so much a library as it was a closet with a reception desk and books at the back.
With such a limited selection, there was no point in asking for relevant sections, or about how the library was organized. Even if there were enough books to make finding one with relevant information on the functioning of what analogy monsters may have to biology, he wouldn't ask out of not wanting to clue in any monsters on the fact he didn't know what might be common knowledge in the Underground.
"Have you heard the news? Dogs pet at Grillby's. Usually, nothing ever happens down here. I've never had to make so many copies before..." A yellow monster in a scarf spoke up from the table. She placed a blank sheet of newsprint over the newspaper in front of her and waved one of her stubby claws over it. A blue light scanned over the papers, copying the print below onto the sheet above.
Magic. He's seen many forms of magic used over his career, but still didn't understand it. Some used incantations, some use artifacts, some used gestures, but magic never made any logical sense. He hated it, and could rarely find the sense in it. Monsters seemed to be able to do it without a second thought. There was very little by way of visual indication as to how the magic functioned.
Pondering this, he looked over to one of the few nearby bookshelves and grabbed a book at random. He opened it.
(Here I am... Writing this book.)
(A person comes in and picks up the book...)
(They start reading it...!)
The rest of the pages were blank.
The yellow monster copying the newspapers spoke up. "Oh hey! Never finished that one. I prefer making word searches and games to actually writing."
"Is there any particular reason why the lines are in parentheses?" Batman asked. It just struck him as somewhat odd.
"I like the way it makes the sentences look."
Clearly, monsters had very high publishing standards.
He put the book back and checked a different shelf, hoping the shelves were divided by content and not only color.
While monsters are mostly made of magic, human beings are mostly made of water. Humans, with their physical forms, are far stronger than us.
But they will never know the joy of expressing themselves through magic.
They'll never get a bullet-pattern birthday card, or merge their magic with someone else's to form a team attack. While our magic is from our souls and are reflections of ourselves, humans are very different when it comes to this. Not all humans have magic. Instead, all humans have faces. Humans usually have arms and legs too, but not all of them do. Even with faces, human expression is very limited. They can move parts of their faces, but they can't change the shapes of their faces beyond what their physical matter allows. They smile, they frown, and they can laugh too, but they can't change the shapes of their eyes or where their noses are on their face. Since this is true for all human faces, they have consistent forms of expression that are universal across all humans.
Batman continued to skim the book. It wasn't particularly well-structured, but it was informative. The author continued to describe what little they knew of humans, then speculated on how humans expressed themselves without magic. It was clear the author didn't know particularly much about humans, but knew a good deal more than most monsters did.
A few important things he noted included the fact that monster food was magical in nature and hence did not need any digestion, and that all of the physical matter in a monster's body was in the dust they left behind after they died. The book also indicated that magic was a regular and important part of monster culture and daily life, and that there were many different kinds of monsters. Still not quite the information he sought.
"Hey!" A high-pitched voice came from behind and below him. He turned around.
A small yellow lizard monster with no arms and a striped shirt that could have been a single oversized sleeve looked up at him.
"Excuse me! There's a book I want but you're in the way!"
The librarian lizard shushed the child, whose voice lowered to that of a loud whisper.
"I'm looking for a book on magic weapons, like spears!" the monster child continued, "Undyne uses spears! She's so cool! Anyways, I'm not supposed to talk to strangers so even though Undyne will beat you up if you do anything bad, I'm still going to follow the rules." The kid scanned the shelves as Batman stepped aside.
"Not that one... not that one... C'mon, I know it was a blue book... Oh! It's up there! Hey, can you grab that book for me? The one on the top shelf there." The child motioned pointedly at the book with their nose.
Batman complied, handing the kid their book.
"Thanks! Maybe I'll still have time to go watch Undyne after I study." The child clamped the book in their mouth before running off.
The kid wouldn't have the opportunity to watch Undyne. It didn't matter how well or quickly they studied, how much they learned, how strong they became, or how much they admired Undyne. They would never see Undyne again. It didn't matter if they were Undyne's admirer, friend, or eight-year-old son. Undyne was gone. And it was his fault.
Nothing he could do would fix this. There was no going back. Only forward. He tried not to think of it, but the thoughts continued to gnaw at him.
He picked up another book.
Because they are made of magic, monsters' bodies are attuned to their SOUL. If a monster doesn't want to fight, its defenses will weaken. And the crueler the intentions of our enemies, the more their attacks will hurt us. Therefore, if a being with a powerful SOUL struck with the desire to kill... Um, let's end the chapter here...
He didn't want to kill Undyne. He'd never intended to kill her. Stop her, subdue her, injure her if necessary but never kill. He'd never wanted to kill, he wasn't trying to kill her. He was certain of that, or so he believed. Could it have been possible that the temptation for the easier path occurred to him, that it was enough to make his attacks lethal? Was he not as in control of himself as he thought he was, as he needed to be? He flipped the page, reading the next chapter, if a fraction of a page could be called as such.
The key to all magic is intent. To control your intent is to control your magic. The intent to make things better is needed to heal, the intent to change something is required to cast enchantments, and the intent to move is essential to fly. Not everyone has the same magic, and there is no such thing as a spell everyone can cast. Everyone is unique, and even if you have the same intention as someone else, your magic will be from your SOUL, and no two souls are identical.
This did provide some insight as to what magic was to these people, but there was still much Batman did not know. He continued reading.
Monsters, at their core, are magic. Magic comes naturally to them because without it, we would not exist. All SOULs contain magic, but a monster's SOUL is made entirely of magic. The complete nature of the SOUL is unknown, but it is the focus of many studies. Especially now.
He wondered if his stance towards magic itself, his disdain for it and aversion to interacting with it, he wondered if that affected how Undyne was affected by his attacks. Would he have to change his stance on magic itself to avoid killing? He didn't like the thought and possibility that was how this magic functioned.
But if intentions were the key to magic, and monsters and their attacks were magic, he wouldn't need to fight back to stop a battle. Only convince them to the point they no longer desired to fight. He could do that.
He resolved to never strike a monster again, and thus remove the risk of any more dust on his hands, and the knowledge that he would succeed with no further deaths filled him with determination.