Hi there everyone! This fanfic here is the shortest fanfic I've made thus far and is already finished. That's right, it's already finished so I'll be able to upload the chapters without any kind of delay holding me back.

The Undertale fandom has exploded and I consider myself being part of that explosion. I haven't made anything remarkable, just been one of those who has spread the word around, shown what a wonderful game it is and watched as the wonderful fandom spread. But I decided to finally do something myself when I realised that I couldn't find a single fanfic with my favourite marshmallow eater even though he and Sans have so much in common...

So here's a fanfic with Byakuran from Katekyo Hitman Reborn!

I have also created a crossover AU blog for this story. I decided to call it 'Flametale'. If anyone is interested in finding out more about what happens after this Underground adventure, then you can go to my blog and check it out. There's a link to it on my profile. I don't have a lot of character designs on the blog, but I've written some stuff.

Warning: Huge spoiler alert for the game Undertale and some for manga of Katekyo Hitman Reborn.

This story is supposed to have many 'plot holes' which the story itself does not explain. It's supposed to have a lot of actions, thoughts and previous actions hidden from you, the reader. I apologise if it seems rushed at times, because I wanted to hide as much information as possible. Please review or write a PM on what you would like to see more of and I might write a one shot about it. I have everything planned, every single detail from start to finish, so please don't be afraid to ask questions. I am certain I have the answer to them all.

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Seven stones... Seven souls... Three pieces... Three parts... So alike, yet so different... One shall have knowledge of both... Two shall make Underground go empty... One with kindness, one with hate... The cycle is repeated... Over and over... Until the true end is reached...

Darkness.

It's quiet except for a single pair of footsteps. In the middle of the room is a patch of grass, lit up by the light from above. That's their goal.

A huge slam echoes in the wide room, signifying the sound of a door closing. A small flower pops out from the ground, a flower with a face as it smiles kindly towards the person who stepped inside the room. The flower seems kind, but they know better that that. No feeling of friendship is between the flower and the person, no matter how cheerful they act around each other.

"Ah, so you're back!" The flower tells the person cheerfully, it's smile growing wider. "I got kinda lonely after you left. Here to visit your old pal Flowey?"

The person laughs softly, a cheerful laugh with no real emotion behind the sound. A male's laugh. The male walk closer, stepping into the sunlight with a happy smile on his face, eyes closed in a way of displaying false trust. The flower knows he's still watching, always watching, so it doesn't do anything. Even with his cheerful aura and his white spiky hair which shines like a gloria around his head in the sunlight, the flower isn't fooled. This man can be very dangerous if he wants to be.

"You are far from my friend. But you're not my enemy either." The man opens his eyes, glancing down at the flower with sharp, purple eyes, those eyes matching the purple upside down crown tattoo underneath his left eye. The man's gaze makes Flowey lean back slightly, wary of him. "I am here merely because I am curious… The singularity changed."

The flower looks away grumpily, an angry frown on its face as if it's looking at someone it really wants to kill. The man goes back to having a cheerful expression when he doesn't get an immediate response, crouching down to Floweys level with his smile easing up slightly.

"I see. So it's the child I just met. That's interesting. I wonder what they'll do with it."

Flowey seems to get angry over this, glaring up at the man with a twisted, evil look on its face. It's not the man's fault this happened, nor is it Flowey's. It's the human who just came here. The human who stole the power Flowey once wielded. Even if the human were to die, that power would never return to Flowey. And that makes it furious. At least it's better than that man receiving the power.

"Don't patronise me! You don't even belong here! You weren't supposed to come here at all! You should be dead and give your soul to me!" The flower starts to smile, eager to see the man shaking in fear. Eager to make this man suffer like he should be. "You don't belong in this world. You shouldn't exist here. Every single person you meet here doesn't know it, but I know you're fake. Everything you tell them is fake. You're just as fake as that mask you're wearing all the time. When I get the chance, I'll rip that mask off you and see what's truly inside you. You'll never be able to fool me, Human."

The man simply laughs at the flower's threat, putting his head in his hand as he's still crouched down in Flowey's level of height. No fear or worry is on his expression, simply a carefree smile like nothing is wrong with the flower threatening to kill him, to literally pull his face off. He's not worried in the slightest, because he knows that's just a far off dream the flower will never be able to accomplish. The flower simply isn't strong enough.

"I'm not hiding behind a mask, Flowey-chan. Because I really have nothing to worry about. You have no chance in being able to kill me. You simply don't have the right determination to do so. It's true I shouldn't be here, but I am. And there's no changing that. This world is very interesting and holds many secrets so I don't mind staying actually."

The white haired man stands up, not being bothered by the furious look on the flower's face. He know it's a sore subject, which is why he mentioned it. 'Determination' is the source of power in this world, and he found it out on his own. He had some time to explore and do research before truly settling down, and there's still so much more he doesn't know. The only one who would be able to know about this singularity is Flowey, but they rather not have to talk with each other more than necessary. Sure, they exchange information, but nothing mind breaking or extraordinary. Simple hints which the other has to muse on alone.

The man adjust the hood of his thick vest slightly, opening his eyes to give Flowey a look that clearly says 'go ahead and try' before he turns his back on Flowey to walk back towards the large double doors leading to the outside. He puts his hands in his pockets, posture relaxed that really screams 'unprepared' to anyone that would want to attack him. But Flowey knows, that man is hard to kill. Even if it's very tempting, he can't attack. That man is always prepared no matter what position he's in. If the flower had human souls, he might be able to kill the male human.

As the doors close behind the man, not a single word of farewell shared between them, Flowey starts to shake in pure rage. That man is very infuriating, always changing tactics, always wearing that smile and can turn dangerous in only the matter of seconds. But never truly offensive or threatening directly. No one should underestimate him, but everyone does so anyway. Only Flowey know what a true danger he is. Not to the monsters who are kind to the human, but to The Plan. The monsters believe he's The One from the prophecy and would never hurt him to get to his soul. He's really hard to kill and Flowey can't get to the other souls either. If that Smiley trash bag was impossible to get past, Flowey is certain it would ever get past that man if Flowey tried again. It believes they are on the same power level. And without SAVE power, Flowey's life can't be kept safe either. Perhaps he can use that new human to his advantage, use that small human to get rid of the man. Manipulate the human who has the power to SAVE that the man is the enemy and not itself.

A large grin grows on the flower's face at the thought of the smaller human killing that man and Flowey standing over his body, laughing over his death. Such a wonderful experience that would be. Even if the human has left the ruins, it will not be the last time that child will see Flowey. Flowey will watch the humans every step and manipulate the human and the monster around the child so that the child will act the way it wants them to. Not to mention that stupid skeleton who listens to Flowey's praises and foolishly think of Flowey as a friend.

"Just you wait… I'll laugh on your grave over and over… Byakuran!"

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Hope you enjoyed the first little chapter. Please don't hesitate to ask me questions. You could ask as PM here or at my Tumblr blog, your choice.

See ya soon~!