The pitch black cave made it impossible for Ruby to tell if her eyes were open or closed. Only soft refractions of light from the water illuminated the walls, but this was a very dim boon for her. After gathering her bearings, she illuminated the area with a small flame generated from her fire magic. The environment was completely unfamiliar. Part of her hoped that, by some miracle, it would just take her back to the entrance to the cave, or maybe even the end of it. Instead, she ended up more lost than ever, and with nobody to guide her.
"Toriel? Papyrus? Anyone?" Ruby shouted, her voice echoing back to her as if to answer her call for life. But nobody else answered back. One bright side to her circumstances was that there was no chance a Chimera would be down there. But that's where the positives ended. It was impossible to tell which direction she was facing, not that it mattered as there were only two directions to go: forward and backward.
So she moved forward, the small flame in her hand being the only source of light aside from the small silver glow in her hand. The water splashing at the movements of her feet was the only thing to break the silence, outside from the flowing water. The Aster Sword formed in her hand, the unsettling dark and silence finally getting to her. Not a single monster dwelled down there from what she could hear. With the army that she saw when the barrier first released, it was safe to assume a majority of the monsters were now on the surface.
Eventually she finally reached a lit-up area, but the joy from the boon was short-lived as she realized the path forward was through an underwater passage at the bottom of the shining lake. Though the subterranean plantlife gave some light, it didn't persist throughout, and there was no way of telling how far it went. The only way she could make it through with certainty was if she knew water magic. But the only magic she could control was fire. Everything else was chaotic and unwieldy.
But unless she wanted to risk either hypothermia or drowning, it was the only way out. Or using wild enough earth magic to break open a path to the surface, which would do god knows what to the rest of the underground, not to mention possibly killing several monsters in the process, maybe even herself.
"Screw it." She said to herself, the Aster Sword in her hand vanishing and the fire extinguishing. She would have to teach herself water magic through trial and error. First thing was first, she needed to learn how to morph water to her will. She waved her hands at the water, hoping that something would come of it, but to no avail. "Okay…" Ruby muttered, trying more forceful movements, yet again with minimal results. The only waves that formed were through her physical exertion.
"Come on, Aster Sword, work with me here!" Ruby tried again and again to get the fundamentals of water magic down, but in the end, her efforts bore no fruit. Without anything achieved despite her practice, she fell to the oddly soft ground and stared at the top of the cave.
"Well, at least Undyne can't find me down here. I hope." Ruby said aloud, her voice echoing back into the cave she came from. Not even a rat made a sound down there. She was truly alone.
Then her stomach growled, and reminded her that there was a time limit. But the more she tried to perform water magic, the less hope she had of ever escaping. Frustration got the best of her, and her arms unleashed a blaze onto the water, hot steam rising from the impact.
"I can do fire just fine! Why can't I do this?!" Ruby shouted out, her breathing heavy from exertion.
"Calm yourself, pupil." An unfamiliar voice said, Ruby freezing in place for a moment before turning to try and find who just spoke. However, nobody was around.
"W-What the-" Ruby said, her nerves shot.
"The army approaches every day, master! I must master its power before they arrive!" This time, Ruby could tell whose voice this was.
"Naimes?" As Ruby said his name, vestiges of two people appeared before him. One of them looked like a younger version of Naimes.
"Paranoia and fear cloud your judgment. Become serene, and one with your inner flow." The unfamiliar woman said. Her appearance was majestic, and her voice calm yet commanding.
"I can't, master! How am I meant to keep the peace if I can't even get this right?!" Naimes exclaimed, the Master guiding his hands.
"The movements are not what matters. Nor is muscle or flexibility, though those certainly do help. No, the mind is the only tool that will master any form of magic. Master that, and you master the elements." The Master said, and before Ruby's eyes, the lake parted effortlessly, without even lifting a finger. Even though it was a vestige, it affected the real world.
"I… forgive me, master. I…" Naimes stuttered, his master touching his shoulder.
"Conventional thinking limits the ways you can use magic. With the Aster Sword in your possession, your potential is unlimited. Perhaps you will be the one who achieves peace for our people." The Master said as the vestiges finally faded. As confusing as it was, it felt like Ruby had more perspective. She felt it when she used earth magic, but it didn't fully click then.
She was too focused on movement, not the thought in those movements. But why did memories of Naimes appear? Going off past events, she only saw visions of the future, but now she was seeing the past play out before her. Would it become more frequent as she adjusted to the Aster Sword, or was this a one time thing?
Nevertheless, it showed her what she needed to hear, but it didn't teach her much of anything. The feeling of harnessing water magic wasn't any closer to her, despite it.
"You're thinking too hard about it." Naimes said within her mind.
"Why can't you just tell me what I'm missing?" Ruby asked aloud.
"Magic is a… delicate art. This age of humanity has long forgotten it, but you will be the herald of the new age, the return of the magic arts. In order to bring about that future, you must learn the ways of magic on your own, without the aid of the Aster Sword."
"So you mean you're intentionally not helping?" Ruby asked, a bit agitated now.
"Would you grow if I gave you all the answers?" Naimes retorted, Ruby going silent, "You have the potential within you to harness light magic, an art that the Aster Sword is exclusive to. For the battles ahead, it is necessary you reach that point on your own."
"What do you mean? What am I gonna be facing?" Ruby asked, remembering the visions from before. A clouded titan, and another shrouded in its own shadow, and a foggy figure that sent chills down her spine just recalling.
"I cannot say." Naimes states plainly.
"Tell me! The lives of everyone are on the line, I know that much! Just tell me!" Ruby shouted.
"I cannot!" Naimes sternly said, his voice forcing Ruby to pause. That told her everything. If he said what she would face, then the possibility of changing the future would be lost. Or at least, something major would change if he did. Either way, she realized it was too big of a risk to know for now.
"Fine. But what good is it if I die down here before I learn water magic? I need someone to teach me!" Ruby said, but Naimes said nothing else the entire time. In frustration, she tossed a rock into the water, with it splashing in her face in retaliation. "Fine! I'll just make my own way out!"
It was only then that she realized how lucky she was that nobody else was around, otherwise she would sound completely insane talking to herself. She looked around for another way out, but the only way outside of the lake was the river she came from, and she already knew there was no escape that way. At least, none that wouldn't simply put her in the same position she was already in.
"Well great… now what?" Ruby sighed, talking aloud to herself as she took a seat on a boulder, trying to think of a way to master water magic on her own. But it seemed impossible. Her fire magic was the only thing she had any control over, and she didn't want to accidentally create a torrent of water that sprayed her face off. If water magic could even be used as a pseudo pressure washer, that is.
Earth magic was a similar case. If something went wrong and she collapsed the tunnel, she wouldn't be able to run anywhere, or if she did survive somehow, she'd just be worse off than she already was. Air magic wouldn't get her anywhere either, so that was a no-go.
The only certainty she had was fire magic, but what could she do with that, she wondered. Unless…
It was an absolutely insane idea… but the Aster Sword gave her magic power far beyond most. Which meant her flames burned hotter than most others. Water extinguishes fire, but if the fire evaporates the water faster, the fire wins in the end. It was a gamble, but she had to try it.
She took a stance at the lake, and concentrated on her magic. Silver shone in her veins in her hands as fire began to coat them, at first orange, then turning blue as the heat built up. Finally, it released as blazing hot flames, scorching the water even before it came into contact. It took hardly any time at all before the water evaporated.
"It worked! Heck yeah, take that Naimes!" Ruby shouted with a leap, practically skipping her way into the newly formed path she made, still feeling some residual heat as she went. Eventually, the cave illuminated again with a fluorescent blue light. Pitch black grass grew on the land around the water, and glowing blue flowers gave off the light in the cave, making the path clear for her to go along.
Among the flowers were significantly larger flowers that only shone dimly, but seemed to glow brighter as Ruby approached them. Curious, she reached out to one, and it sparked in brightness, and suddenly she heard voices.
"...don't know. I don't want another war… but if we go against him…"
The voice suddenly stopped, and Ruby raised her eyebrow at it. It sounded as if this person- or rather monster- was right next to her, where the flower was. She glanced at another similar flower, then reached out for it. In a similar way, it shone brighter and another voice spoke.
"...it all happened thousands of generations before us… I just don't get why he'd hold a grudge when…"
The voice faded again, leaving Ruby only more confused. "Are the flowers… talking to me? Or…" She reached her hand to the one she came across first, curious of what they were doing.
"...don't know. I don't want another war… but if we go against him…"
That finally confirmed it. The flowers somehow were able to copy and mimic conversations that passed them.
"So then… this is a conversation between monsters heading to the surface? Maybe…" Ruby muttered to herself, reaching for a further flower, letting it say its next message.
"...run away. We could try to make peace with the humans, show them we don't have to fight! Isn't that…"
Ruby recoiled at that flower, like it just smacked her in the face. "They… don't want this war? B-But… that doesn't…" She saw only one more flower left, quickly moving to it and touching it. She needed to know the truth of the monsters.
"...will follow us. If anything they might-... no… you're right. We can't keep living in fear and anger like this. For the sake of our race…"
That was all. It didn't explain much in reality, but it gave Ruby a new perspective. There were soldiers in the monster army that didn't want to fight this war. Which meant it wasn't impossible to end the war peacefully. As little as it seemed, this tiny bit gave her hope.
With that now in her mind, she pressed onward through the cave, finally coming to a long wooden bridge. In the distance, she could see a bright red and orange light illuminating the cave, as well as a surge of heat blowing onto her. But there was also a pulse within that heat that didn't feel normal, as if the heat was alive. "Don't tell me there's some lava monster protecting the next area…"
Ruby tried to push that idea out of her mind as she crossed the bridge carefully, seeing a sheer cliff just beyond it. As she came to it, she could feel the lava just beyond causing a sudden wind surge, likely originating from the exit from the underground. For wind to be able to travel this far though, it had to be something else, she realized.
The massive cliff formation just ahead was like a gaping maw looking to swallow another victim, with a passageway just under it, with a narrow rock bridge connecting the two regions. Just beyond it, she could see glimpses of a sea of magma, and just beyond that, an even narrower view of a large metal structure in the distance. "I must be getting close by now. It can't be too much longer at least. Hopefully I'll meet up with Toriel and Papyrus later… but I can't wait around here. Not when Undyne is nearby." She didn't know if she could be convinced, at least not now. Either way, she wanted to try and change her mind.
As she thought that, she could feel a powerful presence quickly approaching her. Instinctively, she drew the Aster Sword again, and felt it drawn to her left. In the nick of time, she parried a blinding fast strike from a spear. The same spear. Undyne tracked her down once again.
After her strike was parried, Undyne stood in a fighting stance at the entrance to the next region. Through her helmet, Ruby could see her glaring eye, staring with an intense hatred at her. "You'll go no further, human! For the sake of justice, I, Undyne, WILL STRIKE YOU DOWN!"
Ruby leveled her sword to Undyne, still trying to find a way out of this fight. But she also thought it might be only possible to communicate to her through their battle. To show her that she had no intention of killing her, or any monsters. "I won't kill you… but I can't back down from this fight! I'll get past you, and stop this war from taking anyone we love!"
The tension between them was more heated than the magma below them. Their first true battle was about to begin, and Undyne's actions made the stakes clear; only one person was walking away from this alive.