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Asriel's Bizarre Adventure: Underground Crusaders

An Undertale Fan Fiction

Starring all main cast of Undertale (almost)

Surface, 20XX

Five years after the liberation of monsters.

Humans and monsters lived with each other with the effort of Ambassador Frisk, the first human who managed to save the monsters from the Underground. When I said the monsters, I also mentioned that everyone is saved, including a certain flower.

Flowey, supposedly a talking flower that plagued the lives of the underground with constant stalking from out of the screen, returned to his former form as a young goat boss monster with the help of Frisk. Frisk saved the boss monster from returning to his murderous flower form by some mean still unknown to most of the casts. With most of his friends spread around the world, Flowey, now using his real name 'Asriel', a teen-aged boss monster, went out from his small, white-painted house full of golden flowers at the front porch and the small lawn.

“Alright, mom, I'm going to school now," said Asriel to his mom.

“In the meantime, I'll bake a snail pie for you, my child," replied Toriel. Despite of having been out from the Underground, she still wore the same model of her blue robe, the one with a Delta Rune around the chest part. She always claimed that it was all for tradition's sake, despite of the monsters not taking the symbol as something revered to anymore, now that the Guardian Angel was revealed to be Frisk.

The walk to his new school was uneventful. It was kind of weird for him to be in high school while he was many times older. But based on Frisk's suggestion (since they met when Asriel was in his original body), he needed a high school to follow up his elementary and junior high education. His mother also told him that his appearance now looked like his father when he was in his teenaged years (minus the yellow hair, of course) with prominent horns and adult eyes.

The high school was a typical brick building that looked old. Seeing one of the murals detailing the memories the school had indicated an old history, dating back to 1930. It only had two floors, but it was far bigger than any buildings Asriel had seen, especially the RUINS. As his mother always said, the RUINS can be pretty small if you get accustomed to it and its puzzles. Of course, now being an archaeological site for the humans, he couldn't go back to his own home.

He went inside and found his class, where he sat where he always sat for some months now. He was then greeted by a young human around his age.

“Hey, Azzy," said the human. “Where's Frisk?"

“Isn't he supposed to be early?" replied Asriel.

“You know what Frisk always do, right? Let me just give you a tip, Azzy. Frisk is getting into a wrong crowd. I don't know what the deal with that gang is, but if he keeps getting himself into trouble, it's game over for him."

“Johnny…he can manage himself. I know Frisk."

“We all know him, Asriel. Look, he may be a hero to your race, but even a hero cannot stay chivalrous forever. Come on, the first course is starting."

Asriel kept thinking about Frisk all day long. Knowing him, he would be a good man, but recently, after a weird nightmare he refused to talk about, he started to become rebellious, even outright beating up a human male who picked up on the boss monster with a wooden stick. He wasn't a bully, it's not in his self. But hanging with street gangs and delinquents made him branded as one, despite of never lifting a finger to beat weak people.

The school was over and he started to get ready for his running club when a monster kid came to him.

“Yo, sans is waiting for you outside. He said it's urgent."

Asriel didn't know what was wrong, but he went to the front gate anyway.

A short skeleton guy, still wearing the same attire as he was 5 years ago, was standing in front of the gate. His choice of clothing started to attract other humans and some young monsters. Despite it being in the middle of a relatively warm spring, he still wore his trusty blue furred jacket and slippers. His wide grin still caught Asriel's attention, and he never looked aged (he's a skeleton, duh).

“hey kid. you gotta go with me to the police station."

“Something's wrong, sans? Is he in trouble again?"

“This is far from his usual antics, prince. right now…he's getting…frisked."

“Sans!"

Knowing this pun-loving skeleton had the same taste of joke with his mother filled Asriel with annoyance. He didn't mean to make any bad things about it, but again, sans was a good skeleton. Well…at least until someone saw his 'true' self.

In the police station, a black and white dog guarded the entrance, lounging by the side while smoking dog treats. Asriel wondered if he knew anything about police procedures. He seemed to be wearing mismatched outfits…again. His appearance made him more like a mercenary than a bodyguard. Still, his sense of motion and smell proved very useful in many situation, given that no one had ever knew that he couldn't see anything that didn't move.

By time, though, he became more serious than before…well, kind of. He's still blind with inanimate objects, so he get tripped many times by some non-moving objects.

“Hey prince…that pet-loving human…he's kind of scary."

“What do you mean, Doggo?"

“I don't know. Something's moving behind him…and it's bigger than him."

Thinking about what Doggo said made Asriel thought, “Is this what I think it is?"

Getting around the holding cells made Asriel uneasy, feeling himself like a bad guy. Just as the human officer reached a holding cell, he saw Frisk.

His hair was still at the same style as it was 5 years ago, and he still had affinity with striped clothing, which made him looked like a prisoner already. He was surrounded by things that weren't supposed to be in a prison, like a television set, and especially, a pistol, which caused Asriel to panic.

“Why do you have a pistol, Frisk?!" exclaimed Asriel. The human teenager then looked up, and come face to face with his adopted boss monster brother.

“Asriel…I am possessed by something."

“Doggo saw something with you."

“I've been possessed by a spirit, Asriel, so don't try to get in here or you'll get hurt."

“kid, we are trying to help you."

“Don't make this even worse, Sans. You know I am not that 'kid'."

Seeing him say like that made Asriel almost snapped. Of course he remembered the 'kid' they were talking about. Even Sans' eyes became serious. He asked the human guards to leave them alone. There were the three of them now, alone.

“Kid, that kid is dead. There's nothing wrong with you. In fact, it's something…"

They were surprised when Frisk started cocking the gun beside him and without warning, shot himself. Surprisingly, the bullet was suspended in mid-air, but suddenly returned back to the pistol as the way it went out. He then shot towards the two and the bullet stopped in front of Asriel, where it returned to him.

Yet what made it more appalling though was the presence of a humanoid figure behind the human. It was ghostly, but very muscular and looking very serious. It had the same face with Frisk in his youth, with eyes closed. It was also wrapped with bandages in some part of its body, and was carrying two wooden sticks on both hands.

When some of the officers came because of the gunshot, they wondered about the gunshot as nothing was damaged, without even seeing the figure behind Frisk. Sans's eyes became all black and he politely asked the officers to get away from the place.

“I'm dangerous," said Frisk. “I have the power to SAVE. Both of you know that, right? But I never thought…"

“Frisk…your power is…something that manifested because of powerful DETERMINATION," said Asriel.

“DETER…MINATION?"

“As a boss monster, because I'm immune to the side effects of DETERMINATION, I can become the Hyper-Death Form you fought…many times. I may not be aware of your SAVE power. You…gave me your DETERMINATION so I can maintain my form and not turning into a flower again. But now…that DETERMINATION also gave me…something."

Frisk was confused by his adopted brother's claim, but was surprised when he saw vines coming out from his hand. It had the same color and form with his nemesis, and he was ready to fight again if Asriel actually returned to Flowey, or worse, becoming the nightmare he fought many times in different timelines.

“Do not be alarmed, Frisk. You saved me from Flowey, remember?" said Asriel with a smile. “This is the same thing you had with you, because of DETERMINATION."

“Kid…," said Sans. “what do you mean by…DETERMINATION?"

“But I thought I…"

“don't jump to conclusions, kid. can you tell me my own power? i am not a boss monster, remember?"

“Uh…you're filled with DETERMINATION?"

One Sof Sans's Eye then glowed blue and he slowly murmured 'Megalovania'. One of his giant dragon skulls suddenly floated behind him, along with some of the bones around him. Upon seeing his eyes, Asriel suddenly felt his body became so heavy, as does Frisk. It was as if they were being pulled by an overwhelming gravity.

“Sans, stop! Don't use your Blue Attack! I am not that 'Kid'!"

Sans then returned to his normal self, and the skull vanished.

“Kid, what if I told you that DETERMINATION is not the only thing that awaken the power you had? In fact, Undyne and Papyrus developed this power, as do Mettaton and Alphys. Undyne is determined enough, but my brother is not so much. Mettaton and Alphys are not even fighters."

“Are you saying to me that this is not even DETERMINATION-related?"

“I prefer it being called a 'Stand', because…they are standing behind you?"

“It's more explained with Frisk, though."

“I'll explain everything. For now…"

Sans activated 'Megalovania' and destroyed the holding cells. If not for Frisk's ability to rewind time, the damage would be permanent. The three of them walked away while some officers, including Doggo, were confused.

At a café, they were eating some food. Sans always have a preference with red ketchup, while Frisk a sweet pie. Asriel…felt like he needed to eat his mother's pie, feeling that she had made it for him.

Just then, they noticed one of their friends came to them. Alphys, now a good-looking yellow-scaled dinosaur monster, walked towards them clumsily while saying 'sorry' all the time when she bumped with someone's table with her tail. She may not be as fat as she was five years ago, but she's still as nerdy as always.

“H-hey, guys," said Alphys while sitting. “I think I can tell you something about…that Stand. You see, this is not the product of a DETERMINATION, and apparently, it has names. Weird, random names, I might say. The person that manifested it can name it from deep between their minds because they are the manifestation of your SOUL."

“Manifestation of our SOUL." This caused Asriel to panic. If the manifestation of his SOUL is the vines, then…

“B-but my 'Stand'…or what the name it is…"

“His Stand are vines," said Frisk flat.

“Frisk!"

Yet this didn't make Alphys feeling scared (at this point Alphys knew that Flowey is Asriel). Instead, she said, “Prince Asriel...your SOUL is a flower's soul for a long time, so of course it manifested as flower vines. Don't worry…Flowey cannot feel happy emotions and you're happy, right, prince?"

“I-I guess…"

“Now, try to find the name deep between your SOULS and said it. For example… 'Big Bang Theory'.

Alphys's claws suddenly made sparks all around it, where she pointed one of her claws towards a nearby television. It suddenly turned into an anime with super manliness, which made Asriel felt…weird. Yet the anime had something that caught their minds, and it was the same ability of power manifestation. One of the characters even shouted 'Crazy Diamond' before another one manifested behind him.

“Well…that's how we sum the whole power. Big Bang Theory can manipulate electronics to do what you desire most. JoJo's Bizarre Adventure is the best representation of what we are dealing right now. Well...something like that."

“Why's that name is Big Bang Theory?"

“Dunno. Maybe it's just…myself? Anyway, let's try it. Prince."

“Uh…'Bed of Thorns'?"

As the same vines manifested on Asriel's arm, it suddenly touched Alphys and Asriel had visions of Alphys's past, something that he didn't know himself. He quickly drew away from the dinosaur, looking stunned, with Alphys wondering what happened.

But then, Frisk didn't answer them, feeling that his SOUL was too big for them to know. What if he accidentally RESET the whole thing again from the beginning, nullifying this event? He knew he had a power called TRUE RESET, and it would be catastrophic if actually happened, knowing that the five years they had spent together would be deleted, and he returned to the moment he fell into Mount Ebott…again, for the last hundred times.

Asriel noticed this. Beside Sans, he was aware of the ability to rewind time. He was aware on how the 'Kid', Chara, his former friend and brother, would kill him in his Flower form, and Sans trying to save the world from imminent destruction. Frisk's DETERMINATION saved him in many ways possible, first by destroying Chara's SOUL inside him, and second, doing the impossible by asking the entity called the 'Player' to do a TRUE RESET, thereby resetting the universe and made everything never happened. When the TRUE RESET happened, Asriel and Sans would never know anything about what happened before it, but Frisk admitted to it.

Asriel put one of his hands on Frisk. “It's okay, Frisk," he said. Suddenly, a power of something he never felt for a while came to him.

He was filled with DETERMINATION.

“Golden…Time…"

Again, the same figure manifested behind Frisk. Asriel and Sans saw it, as do Alphys. Again, not everyone could see it, except a lone child that saw it and walked away.

“Now that the three of you have known what Stands are, let me tell you something really…"

“Oh golly! I'm supposed to come home and eat mom's pie! She's going to be pissed if I don't go!"

Asriel ran away, leaving Frisk, Sans, and Alphys alone.

“Welp…gotta go."

“Alphys, if you want to tell us, how about going to mom's house? She must also know."

Sans walked outside, under the sun. Since leaving the underground, he had no 'Shortcuts', so he felt so lazy to walk and wished Papyrus was there. He really need to make more 'Shortcuts'.

Just then, he felt a very strong killing intention from behind him. He turned around and saw a young kid filled with foul aura. Sans knew the kid wasn't going to negotiate.

“Hey, kid, you don't want to have that aura," said Sans, his eyes went black. “You're gonna have a bad time if you continue."

The kid murmured something inaudible. Sans just stand there, watching the kid while shaking his head. Then, the aura manifested into something Sans knew was deadly.

“K-Kid, you have it too?"

“You may want to stop what you're doing, Sans. We all know you cannot defeat Chara."

“Chara? Oh…that kid with bad CHARActer."

There was no reply, and Sans was suddenly attacked by the mysterious kid with a weird ability not different from him.

“Welp…guess I have no choice."

Sans then manifested his Megalovania and faced the mysterious human. He was as relentless before a reset to a Chara-possessed Frisk (he vaguely remember it, though). Yet this kid was different. Not only did he not attack him with a knife, he actually used the same attack as Sans. They were showering each other with projectiles.

“Are you hoping to RESET all of this, to mend all the mistakes you make? You're targeting me so Frisk will do a TRUE RESET and Chara will possess him. I guess not."

Sans charged his Gaster Blaster. The kid realized what he wanted to do and jumped away before the skull blasted a devastating shot. He wasn't relenting, though. Three more skull came and attacked the human child, but he managed to dodge it, seemingly unaffected by the Blue Attack.

What Sans didn't see was how one of the kids projectiles that missed him turned around and stabbed one of the skulls. Sans felt his head being attack and they started to crack.

“When the Stand is attacked, so does the body," said the kid.

“So you're not affected by it, then?"

“Say that to yourself."

Just then, Frisk and Alphys saw Sans fighting with his Stand. Seeing that he was struggling to fight this kid, Frisk moved in between them and, filled with DETERMINATION, shouted, “Golden Time!"

The same figure manifested behind Frisk and did a controlled RESET, yet it only reset what happened 3 seconds ago, just before Sans got hit by the projectiles. Acting fast, Frisk moved and tackled the short skeleton from being hit. The action broke his concentration and one of the Gaster Blaster hit the human, quickly killing him by disintegrating him.

“w-what? The blaster…killed him? Frisk what are you doing?"

“I RESET the timeline."

“But I killed that kid. he mentioned…Chara?"

“Chara?" Frisk moved sans away from the road. “Good grief…we really need an explanation here, Al."

“Frisk…I killed that kid…"

“It's either him or you, Sans. What's wrong with gaining some EXP? Your LV hasn't gained yet. That kid is not even human."

Meanwhile, Asriel reached his home and greeted by Toriel. Always a caring mother, Toriel asked Asriel his school, then the topic turned to Frisk.

“Frisk had...powers too, mom," said Asriel slowly. “Has he ever told you about his power to RESET?"

“My dear, everyone has known about that. Why is this a problem now, my child?"

“I don't know…it's just…he can use a very controlled version of RESET. Now Alphys told me about this Stand that she took from an anime…"

“Asriel, what did I told you? Don't watch anime with Dr. Alphys and Undyne. Those things are bad influence."

“I know…sorry, mom."

Toriel made a smile. “My child…I don't mean to talk like that. You're an adult now. I don't have a say on that…."

“Actually, we have a say on that, Toriel, and I think you need to know something too, because it is concerning your family."

Alphys' voice from the door startled Toriel, but she calmed down when she saw sans by her side. Despite of having the same taste for jokes, both of them decided to remain friends, partly because sans was too lazy to think about getting a commitment, and partly because of the Overworld. Ever since they left the Underground sans never stayed at the same place, always moving as far as she concerned. Maybe because Papyrus wasn't living in their town, but who knows.

“uh, hi, Tori…long time no see," said sans after seeing Toriel.

“Hello, sans, I've wondered where you might have gone to this time. Are you going to leave again?"

“no…something came up. We can talk later."

“Alright, guys…Toriel, I need to tell you something that's straightforward, blunt, and might get quite emotional. Well, scratch that emotional part, since this is not going to make you feel better."

Alphys made a slight pause and said, “Toriel…your adoptive daughter is still alive."

This made her eyes turn red. “What?" she said.

“Chara is still alive. One of her minions tried to kill sans. Luckily, Frisk saved him before he could die."

“Seriously, Al, that kid had no strong 'stand'-ing ground."

Asriel could see Frisk smiled. The goat boss monster couldn't stand sans' puns, but since it made his mother happy after…Asgore…he tried to bear it.

“Anyway, Toriel, Chara is still alive and she's threatening the world again."

“How can that demon child threatened the world? I know she's a homicidal maniac that killed Asriel once but I thought her body turned to dust. And how can you tell me this in front of Asriel?"

“Because Asriel and Frisk are the only ones that are aware of Chara being a fraction of their SOULs. She's the reason why Asriel was a flower, and she's also the reason why…"

“look, Al, I don't want to cut you off, but I'm the one who knew a timeline where everyone is killed by her."

“I'm aware of that, too, sans," said Asriel. “Frisk destroyed…"

“you may want to stop right there, kid. we are talking in front of Tori."

Asriel realized what he almost did. Toriel didn't know the existence of multiple universes. As Flowey, Asriel was aware because of his brief ability to SAVE. Frisk is obvious, while sans knew everything about it. Alphys had a research data explaining the danger of jumping universes, but not for being aware of them.

After everything returned to normal, Alphys continued.

“sans being attacked proved that you, of all being, are in danger of being killed by one of Chara's minions. It's not that I don't trust your abilities, it's just that you don't want to let yourself get killed, okay?"

“Why is this getting to the point I don't like."

“Yes…Asriel and Frisk must finish everything once and for all. They must destroy Chara's existence."

Asriel and Frisk were surprised by this, too. Alphys was never as blunt as now, and the fact that she never stuttered during that explanation proved that she had grown into a fine monster. Maybe because she's living with Undyne now that her own self was improving.

Toriel was speechless about this, but she stood up, turn around, and said, “Then so be it."

“What? I thought you're…"

“I know what you expect from me, Dr. Alphys, but I've made up my heart the moment I knew Asriel had the power. Now with Frisk having one, too, I cannot stop you from stopping the root of all our misery."

“Why are you doing this? Frisk and Asriel might…"

“That is why, I'm asking Sans to go with them, as does Undyne. That's my only deal to you to let them go, doctor."

“Sans and…Undyne?"

“Tori…you know this is not my dig, right?"

“I know you're far more that capable to protect my children, sans. You've gain LV and HP, as far as I can see."

“But that was an accident!"

“In fact, you still have unfinished business with Chara, am I right? You told us many times about your nightmares with Frisk. I didn't want to believe you at first, but I can see that you want to end your nightmares."

“Tori…"

“Sans, I believe you can do what you must do."

Toriel walked towards Asriel and stared at him for a moment before hugging him.

“My child, promise me that you won't let yourself into danger. Stay with Frisk, alright?"

“Mom…I don't really want to…"

He could feel Toriel's tears running down his shoulder. He knew his mother was trying to hold her tears, but seeing Asriel going from her made her felt sad.

“I will be telling your homeroom teacher that you have an errand to do. Your timing never fails me with the long summer holiday coming. I'll…pack you your favorite snail pie. Just promise me that you will come back, no matter what happened."

“I will…mom."

“Good."

Toriel them let go of Asriel and approached Frisk. The female boss monster also hugged him.

“I never felt this way again for 5 years, my child," said Toriel to Frisk. “You owe the whole Underground a favor for returning my child to me…and being their hero."

“Mom…"

“As much as I doubt Dr. Alphys, she never lies to me, even once. Frisk, Chara may be our child, and we loved her as much as I love you now. But her hatred for humanity and her desire to change the world does not start well. I may be a cold and heartless mother right now, but…I've made up my mind after knowing the truth from Asriel. Frisk, I'm begging you. Don't let Asriel be taken away from us again. Don't let your effort and sacrifice be pointless. Stay Determined."

Frisk couldn't say anything to Toriel before she left them and went to her room. He wasn't filled with DETERMINATION after giving them to Asriel, but decided to follow his heart anyway. He needs more explanation to Golden Time, and finding Chara was the best bet.

Both Asriel and Frisk packed up for their journey. As per sans' request, they packed lightly. During this time, Asriel said, “Hey, Frisk…do you think we should abandon our peaceful life to kill her?"

Frisk asked Asriel about it.

“I mean, you're risking yourself to save me and the whole monster from fear. We just knew when we fight, but you decided to save me anyway. We don't get anyone killed, but…we must destroy Chara."

“Azzy, the only thing that matters to me now is to get rid of that annoying kid. I don't care if my LV will increase after this. After what she had done to me in a different timeline, I won't let her do it again."

“Are you talking about that Genocidal Run?"

“Different universe yields different outcome. A RESET returned the universe to the point of divergence, and that's when I first met you, Asriel. If Chara is alive, then one of the universes resurrected her. Despite the Player's best effort to destroy the SAVE file, I know that unless we fight her head-on, we won't get our true ending."

“You're talking like Alphys now."

Frisk made a smile in his otherwise stoic face. “Do you think I am not paying attention to what you're saying to me hundreds of time? I have better things to do than hanging around with some losers."

“Heh, don't you feel annoyed already? Anyway, don't WE have anything better to do?"

“Let's go, then."

After they went out, they said their goodbyes to Toriel and walked away, without ever looking back. Toriel could only see them from her home, staring at them before turning towards the golden flower Asriel loved to tend. Knowing that they will return home filled her with DETERMINATION.

“Well then, let's go to where everything starts: Mount Ebott."