Previously... The boy takes his stance, and for a moment everything is still, the air crackling with electricity. This fight will be someone's last.
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I rush him, and swipe his legs out from underneath him. Marcie jumps on top of him, a knife above her head.
"WOAH, WOAH, WOAH! MARCIE! IT'S ME!" The boy takes off his bat mask and puts his hands in front of his chest in surrender. His skin is a bit darker than Marcie's, but their eyes are identical. He has a mop of black hair and a cocky smirk plastered on his dirty face. Marceline's eyes narrow and she drops the knife. She stands up and so does he. Marceline turns around, her arms folded across her chest. "God Marcie. You'd kill your own brother?"
"Yes." She walks over to Finn and crouches down. "You alright?"
"Yeah, I'm fine. Just a bruised ego. Nothing I can't fix." Marcie and I shake our heads, and start walking back to camp, happy that we found what we were looking for. He stands up and runs to catch up with us. I turn and look at him. He's a head and a half taller than me, and lanky. He's wearing a red plaid button down shirt, torn up blue jeans and black converse.
"You just gonna leave me here? To my own devices?"
"That was the plan."
"But I'm your brother! Your flesh and blood!"
"That's not what you were saying when you walked out of the door."
"I told you, you could come with me."
"I begged you to stay."
"You know I couldn't." Marcie stops. She turns around and glares daggers into him.
"You could have stayed. I did. I put up with it. You didn't HAVE to leave. You chose to. You left. You didn't want to be there. That was your decision. Not mine."
"Not that I don't like drama," Finn voices, scratching the back of his head, "but we've gotta go back. It's about to get dark. And I don't wanna find out what's lurking out here." Jake barks in agreement and our group starts trekking into the woods. I turn back and look at Marcie's brother and let out a sigh. I nod my jerk my chin in the direction we're going and a smile splits his face. He bounds up the hill we just made our way over and drapes his arm around my shoulder.
"Thanks sweetness." I pick his arm off my shoulder by the sleeve and crunch up my face.
"If you're gonna stay with us, you have to know a few things." I walk to the head of the group, telling him the rules over my shoulder, "First things first, my name isn't sweetness. It's Fionna. Second, no fighting. I don't care what's said. You get physical with anyone here, ever again, you're out. Third, you start a fight, you're out. Fourth, the final decision is always Simon's. No arguing. Fifth," I dodge a branch, and hold it for everyone to pass under and then make my way back to the front, "don't be an idiot." I turn around and smile at him and he rolls his eyes as he folds his arms across his chest. I turn around and we march on.
We get back to the house at nightfall, and we glide through the maze. The new guy seems dazed and confused. We enter the makeshift house and Simon and Bubblegum come out of the lab, both donning white coats.
"You're back!"
"We-we've made a break through!" Bonnie smiles at all of us, but when her eyes fall on the new comer her face drops.
"Hello, Marshall-Lee."
"Hello, Bonnibell."
"Marceline, why is he here?"
"Bunny." She says as she plops down on her stone hard couch. Bubblegum sighs and her hands fall to her side. "Fionna, can we talk?" I nod, and Bubblegum and I walk into her lab.
"What is it?"
"He has to leave."
"Why?"
"He… He just can't be here."
"Why not?"
"He's bad news."
"He can't be that bad." Bubblegum sighs and calls Marcie into the room.
"She wants to know."
"Well, why do I have to be here?"
"I don't know the whole story. You do." Marcie sighs and rolls her head.
"Okay, in order to tell the story, I have to start at the beginning. The guy you met today, is my twin brother Marshall-Lee. Ember is our younger sister, and the baby of the family. And when our mother had Ember, she died. Our father loves Ember, in a sick and twisted way. But he'd never do anything to her. He resents my brother and I, we look just like our mother, so Simon raised my brother and I, as our dad took Ember under his twisted wing. My dad is a business mogul. He runs the biggest scientific corporation in the world. Simon, Bonnie, and her grandma used to work for him. He was making them work on a big project. A project where they were changing human cells. When your uncle discovered that what he was doing, was being tested on humans, he tried to stop it. It… didn't turn out so well. When Marshall-Lee and I turned seventeen, he found out he could leave if he wanted to. We, we argued about it. I tried to get him to stay. But he didn't. He didn't want anything to do with me, or anyone else. He destroyed lives. And I can't, we can't, let him stay here. He'll just destroy your life too." I look at her, understanding exactly where she was coming from.
"It may be a different situation, but I went through that with your sister being here. She'd destroyed my life, but I had to give her a second chance. How long has it been since you've seen your brother?" Marcie's silent. "Exactly. He may have done that, but what if he's seen the error in his ways. Maybe he wants to be here for you again. Have you thought of that?" She's still silent. "Yeah. Now is the time to forget about the past. It's behind us. This is a new world. A new life. A fresh start. Stop holding grudges. It could cost you his life."

*Fin POV*
Fi and Bubblegum go into the lab to talk. I sigh and plop down on the couch next to Marcie.
"Thanks, for earlier."
"Don't mention it. Really. Don't." I shake my head and stand up to talk to Simon.
"What do you think they're talking about?"
"I don't know." Bubblegum calls for Marceline and we watch her disappear. "But it can't be good." We eye Marshall, who's standing in the corner looking around the room. "But it probably has something to do with him." I nod my head and we watch him. He slides down the wall, and brings his knees to his chest. Simon sighs and walks over to him. The two talk in private and I sit back down on the couch. I hear the girls come out, and they all look disappointed and angry. Simon stands up and leads Marshall over to the group. I join them, and stand there waiting for the answer from Simon.
"Marshall and I go back. Way back. Although he has made bad choices in life, he's never been far away from you, Marceline."
"What do you mean by that?" Simon looks at Marshall and nods. Marshall closes his eyes and lets out a breath.
"When I left that night, I was leaving to keep you safe. I heard dad talking one night to someone on the phone. They were talking about taking their testing to a new level. Because we're twins, they were going to use us as guinea pigs in their little scheme. They were going to test our genetics. I left so they wouldn't. I had to wait. If I didn't wait, they could bring me back. But I was never far away. I was always there. I watched you. I fallowed you. I protected you. Do you remember that night you went camping with your "friends"? You got lost in the woods, and couldn't find your way out. You fell asleep. When you woke up, you were at home, in bed. That was me Marceline. I would never leave you. Ever. I was even there for your graduation."
"Who was the valedictorian?"
"Starchie Candymin."
"What award did I get?"
"Marceline, you didn't get an award." Marceline's eyes widen and she bites her lip. I've never seen her this emotional. This strange feeling bubbles up inside my stomach, and all I want to do is hold her and let her cry. But I bury my hands in my pockets and just watch all this unfold. "Marceline, I'm sorry. But I didn't want you to know. You still had hope dad would stop being so mean and hateful. I couldn't ruin that for you. But now, it doesn't matter. But what you have to know, is that dad is still out there. And if we don't stop him somehow, this wasteland, will just get worse."