Authors Note: This is my very first fanfic, so bear with me please. I accept constructive criticism but no hate. If you don't like it, don't read it. I will not waste my time on people who hate me, that is just wrong!

P.S. To avoid any confusion, they are all the same age and grade.

Fionna: 17; junior

Marshall Lee: 17; junior

Gumball: 17; junior

Finn: 17; junior

Marceline: 17; junior

Yes I am adding Finn and Marceline in the story. Finn is her twin brother and Marceline is Fionna's other best friend, besides Gumball of course! Cake and Jake are in it too, but they are going to be animals. Don't judge me, it's my story, I DO WHAT I WANT! Anyways, I know, I know what you're thinking, 'shut up and get on with the story!' But never fear, Arianna is here! Onward! *points out into the distance like a weirdo*

Disclaimer: Sadly, I do not own Adventure Time or any of its characters

Chapter 1: You're a Bully

Ten years earlier…

A 6-year old Fionna is sitting alone in the sand box. Her honey, blonde hair glistens in the sunlight under her bunny eared hat and her deep blue eyes stand out on her pale skin. She happily scoops sand into her bucket. She turns the bucket over, after making sure the sand had set, making a perfect sandcastle.

"Nice sandcastle, Fionna," said a boyish voice from behind her.

She gasps and jumps in surprise and quickly turns. A smile instantly grows on her face as she sees he best friend, Bubba Gumball. Gumball is not really his name but when Fionna met him, he was wearing too much pink. He looked like a gumball. His light blue eyes and strawberry blonde hair and love for sweets only egged Fionna to continue the use of his nickname.

"Hi Gumball," Fionna replied cheerfully, " do you want to help me build a sandcastle?"

Gumball scowled at the nickname. "I don't know, my mommy said that if I get my clothes dirty, I would be in trouble."

Fionna frowned. "Aw come on, Gumball, please. I even brought you an extra scoop." She pouted , holding up the extra scoop.

He sighed in defeat. "Ok, I'll help." He then smiles, grabs the extra scoop and kneels down beside her and starts piling sand inside the bucket.

The two childhood friends sat there happily, not realizing that they were being watched by another little boy from behind a tree. Unlike the two friends, this boy wore a scowl on his face. His gray eyes turned stone cold as he watched the two. He had ebony, unruly hair and pale skin, even paler than Fionna's, making him seem almost ghostly white. He blended almost perfectly into the shadows.

The boy watches as Fionna looks up at a butterfly as it floats by.

"Oh, Gumball, look at the pretty butterfly," he hears her say as he watches her get up and start chasing after the delicate insect, trying to catch it with her bare hands.

Gumball looks up from where he was and smiles at the sight of silly best friend.

"Fionna, you're never going to catch it." Gumball teases with an amused smile as Fionna glares at him.

"Oh yeah," Fionna challenges, "watch me." She turns around from him and continues with what she was doing.

While distracted, Gumball did not notice the strange shadow boy sneak up behind him until he found himself covered in sand. The boy had gone up and kicked Fionna's and Gumball's perfect sandcastle at Gumball.

Gumball's eyes start to water as he had gotten sand into them. The boy noticed this and starts to laugh a cold laugh. He picks Gumball up by his collar, only to shove down onto the sand.

"Ow," exclaims Gumball having scraped his elbow while trying to break his fall. He starts crying even more. The boy only continues to laugh.

Noticing Gumball's cry, Fionna turns around to see her best friend in tears and boy who she does not know laughing at him. Her face flushes a cherry red and her cheeks puff out in anger.

'No one is going to hurt my best friend,' thought Fionna as she stomped her way over to the two boys.

"Hey!" she yells as she pushes the laughing boy away from Gumball, causing him to fall. "Leave him alone!" She holds out a helping hand to Gumball. He sniffles and takes her hand allowing her to pull him up.

The shadow boy scowls at Fionna. He gets up and pushes Fionna.

"What the flip, dude! What's your problem." Fionna crosses her arms and glares at the boy as Gumball hides behind her.

"You're in MY sand box, that's the problem." The boy mimics Fionna in crossing her arms and glares back.

Fionna scoffed. "YOUR sand box?! What the flip are talking about? It's not YOUR sand box, it's EVERYONES sand box."

It was the boy's turn to scoff. "Oh yeah," the boy challenges, "Then why does it have an M on it." The boy smiles smugly as he points at a place in the corner of the box. "M for Marshall Lee." The boy says obnoxiously as eyes light up victoriously. He crosses his arms again.

Fionna huffs and at looks to where he is pointing. Sure enough, there is a large M scratched onto the wood that is the sand box.

Fionna glares back at the boy now named Marshall Lee, hands on hips, and opens her mouth to say something when Gumball interrupts.

"That-"

"Fi, let's go. I don't want any trouble." He glances at Marshall Lee. Surely Marshall was more than capable to beat him up. 'And Fionna' he added.

Fionna's features softened at the sound of her best friend's frightened voice.

"But… he hurt you." She stares daggers at Marshall, who only smiles smugly in reply.

"Please," He looks at her with pleading eyes.

Fionna sighs as she shoots Marshall another piercing look. "Ok, we'll go."

Gumball sighed gratefully and takes Fionna's hand in his. Fionna's face flushes red again, but from embarrassment. Gumball never really holds her hand. He starts to drag her away when Fionna suddenly stopped.

"What about our stuff?"

"Leave it. Let's go!" Gumball tugged a little rougher this time, desperate to leave but Fionna stayed put.

"Gumball!"

"You should listen to Gumbutt over here. It's not like you'll need it." Marshall drawled and to emphasize his point, he sat down and started using their stuff.

"His name is Not Gumbutt!"

Marshall only shrugs and continues on with his playing.

"You're a bully!" was the last thing Fionna said to Marshall as they left the playground.