Peter whipped to face Chara. "Wait... your best friend and basically adopted little brother is a maniacal homicidal FLOWER!?"
Chara's face was pale. The pink had left her cheeks. "I... I... oh no, no no no, he can't be! He's not like this!"
Peter looked at the floating goat demon hovering off the ground, bathed in a myriad of rainbow colors, eyes flashing with hatred.
"Uh... I think he already is."
Asriel laughed, and sent rows and rows of flames, each burning brighter than the sun. It was all Peter could do to dodge him.
Chara was curled up in a fetal position, softly shaking. Peter wanted badly to help her, but this guy wasn't messing around. He shot a web at him, but it disintegrated before it hit. He followed up with a punch, but Asriel just tossed him into a wall.
Raising his arms, Asriel summoned meteors of literal stars. As they hit the wall of the barrier, they exploded into more. Peter wasn't fast enough to dodge them all, and he got hit hard.
"...Oww..." He got up. "Chara, I need your help. Please."
She was chuckling between the shaking. "I can't believe it... he used to joke how he'd become the absolute god of hyperdeath... and now he is..."
Peter went to shake her shoulders, but she was still intangible. "Chara, what do I do!"
She smiled sadly. "Nothing. You'll just die. He's literally unbeatable now."
Asriel summoned lightning from the sky, crashing into Peter. He felt his SOUL split in two, and thought of his friends, both underground and above, who were counting on him. This guy was worse than Thanos! What happened if he left here!
"I can't... let him... win." Peter grit his teeth. And his SOUL?
It refused.
He was back facing against Asriel, who seemed slightly surprised, but overall dismissive.
"You know... I don't want to rule this world anymore." Asriel shrugged. Pulling blades made of pure rainbows, he slashed at Peter, nearly splitting him in two.
Peter rolled to the side. "Why the theatrics then? Why not just let everyone go?"
"Once you're dead, and I have control of the timeline, I will." Asriel shook his head. "I'll just reset. Be back with you, and mom, and dad, before all of this. I can do that now!"
He pulled out a giant laser. "All your progress... everyone's memories. I'll put them all back to zero!" He blasted again, and again, and again. In one final blast, Peter was surrounded by a beam of light, destroying him instantly...
But he refused to go down.
"WHY!" He yelled. "What to you gain from all this?"
"Then we can do everything ALL over again!" Asriel laughed. "All those memories, all that time... you'll make them again!" The swords were back, and Peter flipped over a ledge to avoid them, finding himself near the crumpled body of Chara.
"This isn't him at all..." She whispered over and over. "This can't be, must be a dream... this is all my fault... this isn't him..."
"Then you know him! Help me outmaneuver him! What can I do?" Peter asked. "Please, for the sake of everyone, I've gotta beat him!"
Asriel called the stars once more. "And you know what the best part of all this is? You'll DO it. Then you'll lose to me again..."
Peter died, but walked it off.
"And again..."
He felt his determination grow.
"AND AGAIN!"
Stars rained from the heavens, lightning flashed, and swords struck, but Peter didn't lose hope. He died again and again, but he grit his teeth and pressed on.
"Because you want a happy ending..." Asriel grinned. "Because you "Love your friends." Because you never... give... up."
Peter smiled through his torn mask. "What can I say... I've learned from the best.
Asriel growled, and unleashed more chaos. Peter rolled and leapt to dodge it, but still caught several bullets to the face, and some lightning to the chest.
"Isn't that delicious?" Asriel shook his head. "Your determination. The power that has let you get this far... It's gonna be your downfall!"
Peter felt he had a point. He had no plan, no weapons, no words... But he did have backup. She just needed a little push.
"Chara, please... help!" He said to the ghost girl.
She opened her eyes, and clenched her fists.
"Now, time to purge this timeline once and for all!" Asriel laughed as a huge skull blaster appeared. It pulled in chucks of the very universe, then spat them out in a huge blast.
Peter felt himself slipping...
Till someone grabbed his hand. Peter still felt the beam, but somehow, his DETERMINATION was amplifying far above normal levels.
"... even after that attack, you're still standing in my way...?" Asriel sounded surprised. "Wow. You really ARE something special."
Peter looked at his hand. "Not sure it's all me..."
Chara blazed with DETERMINATION, and clenched her hand in his. "He may no longer be the person I knew... And it may be all my fault... But I'm here to help you stop him! Whatever it takes!"
Asriel couldn't see her, apparently, because he said, "But don't get cocky. Up until now, I've only been using a fraction of my REAL power!"
"How anime of you." Peter grinned.
Asriel snarled. "Let's see what good your DETERMINATION is against THIS!"
He warped reality, and when everything reformed, he was a giant, winged goat-thing, with massive horns and bigger shoulder pads.
"Very metal. Should I be scared of your singing voice?!" Peter yelled. Suddenly, he was pinned in place, unable to move. "Gosh, you're... AGH, high pitched."
Asriel laughed in a super-low octave. "Urah ha ha ha… Behold my TRUE power!"
Peter couldn't move as wave after wave of bright beams sliced through him. "The irony of my last quip doesn't escape me, by the way-"
He died, and when he returned, Asriel was laughing.
"I can feel it... when you die, your control on this world slips away a little more." He grinned. "And when you return, your friends remember you a little less! You'll die here, in a world where no one remembers you!"
Peter grit his teeth and willed himself to move.
"Still, you're hanging on...? That's fine. In a few moments, you'll forget everything too. That attitude will serve you well in your next life!"
He hit Peter again and again, but Peter refused to lay down and die.
"Still?" Asriel laughed. "Come on, show me what good your determination is now!"
Peter couldn't move. Everything was going black. But the blazing light of Chara's DETERMINATION didn't falter, and slowly he felt the will to move return to him.
Then Chara noticed something. "We've been going and saving the story, I suppose, every time we focus our DETERMINATION on a specific point... Maybe, with the DETERMINATION we still have... we can save something else!"
"Or... some... one!" Peter got the idea. In his mind, he saw through Asriel to his friends. If he could save them... then he could cut through Asriel's power!
The skelebros were first, and he found himself face to face with them, except... they looked like they were forgotten, somehow.
"Sans! What kind of instrument does a skeleton play? A trombone!" Peter yelled.
Sans smirked a bit, then his smile faded. "Just give up, kid. It's what I did."
Papyrus gnashed his teeth. "NYEH! I MUST CAPTURE A HUMAN!"
Their attack came, but slowly. Peter could dodge it.
"Papyrus! Care to stump me with a puzzle?"
Papyrus went to help him, then paused. "WAIT... HOLD ON..."
"there's no hope." Sans said sadly.
"How about some... pasta!" Peter yelled. "It's impastable to resist!"
Papyrus groaned, but was clearly overjoyed.
"i can never see them... ever again." Sans groaned.
"C'mon guys! Remember all the fun we had!" Peter yelled. "We're friends! I couldn't have gotten here without you!"
Papyrus snapped back to reality. "WAIT, NO! YOU ARE MY FRIEND! I COULD NEVER CAPTURE YOU!"
Sans chuckled. "nah. i'm rooting for ya, kid. you go this."
They vanished into mist, and Peter turned his attention to Undyne. Grinning, he gave her a light punch. She dropped into a defensive stance, but couldn't help but grin.
"Death to all humans!" She yelled, but her heart didn't seem into it.
Peter lightly dodged her spears, gave her a stunning smile, and kicked her into a wall.
She seemed to recognize his fighting style. Standing up, she dusted herself off, and her memories all returned. "Well, not all humans are bad, eh ya punk! Go help the others!"
Peter watched her vanish, and reached out to Alphys next. "Hey Alphys! What's your favorite cartoon?"
Her face lit up. "Kissy Kissy Mew- wait... no... you hate me! Don't you..."
Peter shook his head. "No, I don't! You're my friend! I want to help you!"
Alphys blinked. "But... I've gotta keep lying..."
"You're better than this! You can be better! I believe in you!"
She snapped back to reality. "Peter!? Omigosh, you're right! My friends believe in me, and I believe in you!"
All that was left was Toriel and Asgore. Peter reached out to them.
"Mom! Dad!" Chara called out. Peter felt their shared DETERMINATION rise even more.
"Your majesties! Wake up!" Peter yelled.
"Forgive me for this..." Asgore spoke.
"I'm doing this for your good!" Toriel insisted.
Peter dodged their fireballs. "Hey Toriel! Remember that my favorite pie filling is cinnamon?"
Toriel blinked, but the two kept throwing fireballs.
"I won't fight you guys! There's a better way!" Peter yelled.
This clicked something in their heads, snapping them awake.
"You are our future!" Asgore called.
"And your fate is your own!" Toriel added. "Go and save us all!"
As they faded back, Peter could feel Asriel's SOUL resonate with the feeling of hope and dreams again... but there was something missing.
"I don't understand!" Peter yelled. "I saved them all! Who could I be-"
Chara and he suddenly looked at each other, nodded, and then spoke as one. "ASRIEL!"
Asriel blinked. What are you!-"
Peter felt for a moment, and suddenly, Chara's memories flooded his head. How she had fallen, how she had met Asriel, how they had been a family. Peter felt her pain, her hopes, her love, her fears, her past... And he channeled it all towards Asriel.
Chara blinked back tears and thought harder. How much she had loved her family. How it had pained her when she hurt Asgore, and Toriel… and Asriel. Her anger towards humans, but her friendship with Peter. Everything that had happened, everything she had learned, every step, every mistake, and Asriel suddenly realized everything as all her memories of happier times flooded into him.
Peter added his own. A midnight swing through Manhattan. A gaming session with him and Ned. His last embrace with Tony. His first kiss with MJ. And all the things he had experienced in the Underground: Toriel hugging him, Papyrus' disaster hangout, lunch with Sans, the concert with Shyren, Undyne giving him a friendly noogie, Alphys and him geeking out, his dance off with Mettaton. And how he and Chara had talked, sitting in front of a haunting music box while the rain fell overhead...
"What... what did you do!" He cried, shaking his head. "What are these feeling!? What's happening to me?"
"ASRIEL!" Chara called out. Peter knew Asriel couldn't hear her, so he called out as well
He shook his head. "NO! I NEED NO ONE!"
He unleashed a hail of light. Peter stood tall, Chara next to him, their shared DETERMINATION glowing even brighter.
"ASRIEL!" They called out again, Chara's emotion mixed with the earnestness of Peter.
"STOP IT! GET AWAY FROM ME!" He cried once more. "Do you hear me!? I'LL TEAR YOU APART!"
Peter didn't move. He only yelled louder, Chara's voice mixing with his until she felt almost tangible, almost real again.
"ASRIEL!"
Asriel began to drip hot tears. "Chara… don't you know why I'm doing this...? Why I keep fighting to keep you around...? It's because you're special! You're the only one that understands me!"
Chara was crying too. "Asriel, I died for my own arrogance, and fear, and hate! You have to let me go!" Peter yelled. Or was it Chara?
Asriel grit his teeth, shaking his head. "You're the only one who's fun to play with anymore..."
"Let me go!" Chara yelled. Or was it Peter? He couldn't fully tell anymore. "I'm sorry! For everything! For all the stuff I told you, for every time I insulted you, or belittled your kindness! This isn't you! Please stop!"
"But I'm doing this because I care about you!" Asriel yelled, fireballs falling like tears. "I care about you more than anyone else! I'm not ready for you to leave, to say goodbye again! For this to end..."
Chara shook her head. "Everything must come to an end."
"JUST LET ME WIN!" Asriel shot a beam of light at them. Their determination flared, even as Peter felt his health lower and lower.
"STOP!" He yelled. The flames turned to a light rain.
Chara's eyes glistened in the light, and she began to let her DETERMINATION return to normal levels. Peter gasped as he realized that, for a few minutes, the two of them had been sharing his brain. That was odd.
"PLEASE!" Asriel cried. "Chara, I'm so afraid and alone and..."
Asriel began to weep. A bright light encompassed the battlefield, and everything went white.