Frisk wanted to keep running away but had already learned that wasn't very conducive to calming her down. So he reached further in his JUSTICE magic and aimed his bow. Two pseudo-arrows were shot in the span of a second, this time he hoped to capitalize on the arrows ability to destroy her water spears to land a meaningful blow against the armored opponent.

Undyne moved to block with her spear, but this time, the arrows were on target; the first would disperse her spear, and the second would hit her unarmored head. Frisk doubted it would do too much damage, but he had to show he was serious in this fight. The best way to do that was to at least trade some blows.

"Wha-" The human watched as Undyne aborted her attempt to block and almost instinctively threw herself to the side, easily dodging both attacks.

"Nice try Human! But your tricky attacks won't work on me." She bragged instead of capitalizing on his surprise. Reaching up, the Captain of the Royal Guard held her glowing blue spear in the air before slamming it into the ground. "You're fighting against the hero of the Underground!"

"You fight well, but I wouldn't call you a hero." Frisk shot back as he readied another arrow to fend off whatever attack his opponent was planning. "Wouldn't a hero try and break the perpetual cycle of violence between humans and monsters?" He packed more JUSTICE than ever into his readied arrow.

"Shut Up!" The water-like energy swirled and grew beneath Undyne before her JUSTICE mixed in. Lines of glowing yellow spears exploded from gathered power and hurtled towards the target of her anger.

Frisk released his charged arrow, and the two attacks collided in the air between them. The opposing electric and water-like magic crashed into each other and detonated. Both fighters stood their ground and watched each other through the explosions after effects.

Frisk was actually slightly surprised after realizing the blasts were equally matched. Undyne might have him in skill and speed, but their magical strength couldn't be that far off.

"You couldn't understand the pain of being trapped down here for our entire lives!" Another yellow spear formed out of the magic beneath her, but she didn't shoot it at him this time. "I fight so our King can free us from the prison you humans put us into." Frisk dismissed his JUSTICE and infused his Aura with PERSEVERANCE, hoping to take the enemy off guard with his durability.

They charged, and Undyne reached him quickly. Using something he learned from his lessons with Toriel, Frisk condensed a sphere of purple flames in his right hand. He hoped to tank the blow and deliver one in turn.

Unfortunately, once again, the warrior seemed to realize his intentions and used her yellow spear to deflect his right arm instead of just attacking him. Frisk, now overextended, took an INTEGRITY-enhanced armored elbow to the stomach, launching him back into one of the snowy tree trunks.

"Gah!" His fake Rasengan died in his hands as he felt the blow, even through his Aura. He immediately started to get up, his mind desperately trying to think of why all his plans were failing. It almost seemed like Undyne remembered their previous fight, but was that really possible?

No, it didn't matter right now. Frisk still had to continue with his plan, which might have given him another idea. "Is that really what everyone wants, to keep fighting each other until one of us dies?" He tried using the same line as before, while she might not remember it completely, maybe something would get through to her. "Is that really what you fight for?"

For a second, Frisk saw the determination in her eyes waver… DETERMINATION! Maybe that was why Undyne was able to predict his moves like she remembered their last fight. The Captain of the Royal Guard was always known to have the most DETERMINATION of the monsters in the Underground. It was just a theory, but it did make sense to him. He was getting through to her because she was having Deja Vu because of their argument in that discarded timeline.

Which meant he had to take advantage of it quickly.

"I know that I can only understand a fraction of that pain." Frisk had only been trapped here for… wow, how long has it been? It was difficult to keep track of all the resets. "But I'm still going to try and make it right! My goal is to free everyone, and I won't let you stop me!" His eye blazed with purple energy as he gathered PERSEVERANCE in his right hand.

This time, he charged forward with his spear forming mid-lunge. Unyne blocked it relatively easily, but Frisk did not overextend, so he wasn't blown away instantly. They entered a fierce close-range battle, where the human was forced on the defensive almost immediately. The difference in their speed and strength was too great. Not to mention that Undyne outclassed him in spear technique as well.

Frisk was basically self-taught in the art of the spear; his only formal training was sparring with Papyrus. While the skeleton wasn't a bad teacher, he couldn't hold a candle to Asgore, who had personally trained Undyne in spear combat.

So Frisk took hits, his Aura the only reason he could stay in the fight. Without JUSTICE enhancing his speed, it was all he could do to slowly allow his flame-enhanced Aura to drain away. Even trying to kick with gravity-enhanced power, courtesy of his ballet shoes, did nothing against the juggernaut.

"Let's see how your perseverance holds up to this!" Undyne swept her spear in an arc, and the human just barely managed to bring his spear to bear; the two opposing Magic Weapons hissed as fire and water fought against each other. The sheer force of the swing managed to lift Frisk slightly off the ground, and the more experienced spear user took advantage of his lack of leverage to score multiple quick thrusts.

The attacks left Frisk off balance, which was compounded when she slammed her armored foot into the ground and her form blurred blue, suddenly appearing to his left. It wasn't some sort of teleportation technique; she was just reducing the weight of her armor and moving fast. Multiple jabs of the spear later that he barely managed to defend and her form blurred once again.

This tactic worked even better for Undyne. Even with enhanced durability, his Aura was dropping quickly. He needed to do something fast.

Frisk ducked Undyne's next strike and rolled his spear to the crook of his elbow. With a clap, he brought his two hands together while channeling one of his opposing soul traits in each. Pushing that power into the ground, he watched his enemy's eyes widen, and she immediately jumped away.

The human did the same and watched as the earth erupted between them. That would only buy him seconds of time, and only because Undyne would be wary of any repeat attacks if she charged in. Frisk clenched his spear and thought hard. He needed some way to match her speed while maintaining the durability necessary to compete in close combat.

He couldn't use both soul traits to enhance his Aura simultaneously. He still didn't have the control to combine both elements without exploding, so without those, he was left with his shoes for magic.

Well maybe…

Watching as the dust settled from the detonation, Frisk studied Undyne across the small crater. Maybe her speed wasn't just from reducing the weight of her armor. That stomp she did when her form blurred was similar to what Papyrus did when he wanted to increase gravity with INTEGRITY magic.

Deciding to try it, Frisk raised his foot slightly and 'kicked' the ground with the ballet shoes. He had already known the enhancement only activated when he kicked something, but what exactly kicking was seemed to be broad, at least according to whatever logic the shoes ran on. Because Frisk was launched forward almost as quickly as he would be enhanced with JUSTICE magic.

He soared over the small crater and thrust his spear at the enemy. Undyne, caught off guard by his sudden leap, barely deflected the flaming spear. Though it did manage to singe her cheek with how close it got.

Landing awkwardly behind the stunned warrior, Frisk managed to not fall on his face, before he turned around. "I think my PERSEVERANCE will hold up just fine." He twirled his spear with renewed confidence. He might be exhausted, but he could tell she wasn't 100% either. "How will your INTEGRITY last while fighting someone with the same goal as you?"

Undyne flinched, and Frisk knew he had struck a nerve; the bubbling blue aura around her armor even dipped slightly. "I want to save everyone down here, the same as you." His right eye burned a stronger purple as if in confirmation. "I even understand wanting revenge, and if the humans who trapped your kind down here were standing behind me right now, I honestly don't know if I'd stop you."

Before he could continue, Undyne charged forward. "You're lying!"

She said that, but the aura around her armor had weakened. This didn't make it an easy fight, but it did make it more fair. Frisk was still slower in actual combat, though with her INTEGRITY weakening, Undyne's armor was starting to slow her down and reduce that gap.

"You don't actually believe that." Frisk's Aura flickered as he barely dodged another blow. Actually, using the shoes during combat was challenging to get the hang of. "You can see the truth in my magic just as I can see it in yours. You can't convince yourself that this is still the right thing to do."

"You're wrong!" Undyne threw her spear of yellow energy, and Frisk was forced to sacrifice his own weapon to stop the attack; even then, it still blasted him back. Slamming her hands into the ground, she created a giant whirlpool of blue energy at her feet from her own magic. Once again, spears started to explode from the swirling mass; more than thirty spears attacked him from all directions.

However, this time, they weren't enhanced by JUSTICE. So Frisk dug into the last stores of his JUSTICE magic to create an omnidirectional blast of electricity that disrupted each spear and made the attack useless. The human sighed in relief and almost fell to his knees from his overuse of magic.

Undyne looked at the triumphant human with conflicted eyes. "I-I have… Asgore's plan still needs your soul to break the barrier." The remnants of her whirlpool formed a single blue spear in her hand. "If you make it past me, the King will be forced to fight you." She dashed forward and thrust her spear.

Frisk panted as he stood back up and manifested more purple fire into his hands. He didn't have enough for a full spear. But his opponent's attack was slow compared to what she was capable of, so the human could grab the spear as it was thrust at him. The blue and purple energy clashed once more.

He was losing, and his Aura flickered like a light. But Undyne wasn't even using her own conviction anymore. She was just pushing herself forward for Asgore's plan, which meant his meta-knowledge was actually helpful for something.

"Asgore doesn't even want to go through with his plan!" Frisk's Aura shattered, but the flames of PERSEVERANCE didn't leave his hands. The blue spear dug into his skin, but he didn't falter. "H-he could have absorbed one of the souls and crossed the barrier to gather more any time he wanted."

The pressure behind the spear vanished as Undyne backed up as if physically struck. "Wha- That can't be right! His plan is the hope of the entire Underground!"

Frisk coughed and slowly brought his bleeding hands up. "Isn't it his job to give his people hope?" He asked but didn't wait for an answer. "Can you truly tell me that the Asgore you know would relish the chance to bring down vengeance upon anyone?"

Something flashed through her eyes, and Frisk knew she believed him. The King might act scary, but he was actually a big ball of fluff, kindness, and incredible guilt. "That's all we have, all I have, to believe in a better future," Undyne muttered, trying to come to terms with what she had heard. "Without that… what happens?"

"I don't know." Frisk brought his damaged hands forward to make half the Seal of Reconciliation… So what if he knew how to do it? He was a weeb, too. "But I know we can try to do whatever it is together."

The heavily battle-damaged forest was silent as everyone waited for her response. Even the skeleton brothers watched the scene without a peep.

Undyne's spear melted into the ground, and she slowly reached out to hook her fingers around Frisk's. "I-I guess I could use the help, trying to figure something out and all." The two fighters completed the Seal of Reconciliation. "You're not too weak, I guess, and it should be easier with more than one strong person working on it."

Relief flooded through Frisk as the last drops of PERSEVERANCE magic left his body.

A/N: Aloha! I hope I did the final fight between him and Undyne some justice. There were some things I wanted to add but couldn't really find a way to when writing the fight. Still, I hope it was at least somewhat satisfying. Frisk was never going to beat Undyne through sheer force; he's still weaker than her, after all, and unpredictability can only go so far against a skilled opponent. I hope the purposely being Chunni and like an anime protag came off as funny and not annoying.