I don't own Adventure Time. Just so that's out of the way...
This "Finnceline" story is supposed to be different from the others. I've read some good ones. But I don't want it to have the awkward situations in basically the first paragraph where people just put "lemon" and make the story kind of odd to read. I intend for it to have more... feeling in it. Also I made the dialogue easier to Follow. Because I always hated not knowing exactly who's speaking. Enjoy.
Marceline Abadeer had always been someone who enjoyed her privacy and time alone. Being a vampire for most of her life being alone was almost habitual. Over the 1,000 or so years of being alive (or not) she had experienced much loss. From friends to dear loved ones, she found herself trapped in the spiral of death and couldn't care less. Perhaps one of the biggest triggers for her manic sadness and apathetic behavior began when she was a little girl. Her father was never around due to "business" in the Nightosphere and she doesn't really know anything about her mother. All she's ever heard about her is that she is "in the sky" now. Marceline never thought much about that though. Also, The Great Mushroom War was another trigger that mentally scarred her and the only person she had met for many years, Simon Petrikov, lost himself in madness from some sort of extreme schizophrenia. Her life never seemed to give her just one break. After many failed relationships starting around the young age of 650 she finally met a man named Ash. They had an on/off type relationship and for the longest time she thought he was the one but she was only fooling herself. He treated her almost like a slave; he had no respect for her and only ordered her around. She put up with it because she always knew that he could maybe one day change, and because she had no one else that cared for her. After a terrible breakup with Ash due to him selling her beloved Hambo, which was given to her by her long-lost and dear friend Simon, she decided to leave her entire world behind for a few years to explore the land of Ooo and free her mind from all of the depressing memories full of neglect and mistrust that came from her tree house and the cave which was the only place she knew of nearby that she could always go to as a mental escape. After her many years of travel and adventure she finally felt like her pain was numb and she felt like she could finally start to move on. Although she always felt lonely, as if Ash took a piece of her heart and threw it away, like something wasn't right. Then she met Finn the Human.
Marceline was at her home playing her demon blood-colored battle axe bass on a normal day like any other. It was about 4 in the afternoon so Marceline was exhausted from staying up all day playing her bass and pouring her heart out with singing because for the third day in a row she just couldn't sleep. It was very obvious too. She had worn the same gray sweat pants and black tank top for the entire duration, her hair was messier than usual and she had bags under her eyes. Marceline was depressed but always had hope, she was mentally strong and she knew it but sometimes she wished that she wasn't.
M: "Man I need something to do…" Marceline said in a depressed tone and a sigh. She started to look in her phone and went down the list of people's numbers that she had.
M: "Bonnie, Dad, Finn, Jake…" her voice trailed off realizing that she didn't have many people that she was close to. She decided without thinking due to her lack of sleep and dialed Princess Bubblegum but quickly hung up.
M: "Yikes! I haven't talked to P. Bubs since… well, maybe now isn't a good time." She said with a hint of nervousness in her voice and a slight rosy blush in her cheeks. Then she thought to herself that she hasn't seen Finn or Jake in a while and considered calling them. Suddenly her phone rang and to her surprise, it was Finn.
F: "Marceline!" Finn yelled into the phone.
M: "Hey Finn what's u-", she was cut off by muffled sounds of Finn screaming and the loud sound of metal slamming together and loud slashing noises.
F: "Run Jake! There's too many!" after a brief moment of hearing the panic over the phone with what sounded like Finn and Jake running and strategizing how to defeat some sort of horde of enemies Finn answered the phone sounding as if he just sprinted a mile.
F: "Hey, Marcy… me and Jake kinda… need help." Finn said as he was struggling to slow his breaths while speaking.
M: "Finn, what's going on are you ok?!" Marceline almost yelled that into the phone with the thought in the back of her mind that her history of loss would repeat itself with one of her closest friends.
F: "Yea, me and Jake are sorta-"
J: "It's Jake and I dude!" Jake said quietly yelling.
F: "What? Nah man, that just sounds weird."
J: "It sounds weird? Finn, did you eat your breakfast this morning?"
Finn and Jake kept arguing about pointless things one after another for about 30 seconds until Marceline yelled into the phone and demanded what was going on. Finn proceeded to tell her that they somehow raised all of the undead in the evil graveyard from the badlands and they were being chased by about 300 zombies, skeletons and lifeless creatures.
Without any other ideas Marceline told the two to bring the undead horde to her cave so she could help fight because it wouldn't be a good idea for her to fight out in the sunlight.
F: "Ok Marcy, that's good cause we're already here! Globbit they're fast!" Finn yelled as he hung up the phone.
And with that Finn and Jake got to Marceline's cave about 10 seconds later and without any words the three started fighting in perfect unison. Jake turned into a much larger version of himself and began smashing their undead foes with his giant fists and Finn was already hacking and slashing away with his Demon blood sword. Marceline didn't bother transforming into anything because she knows all of the weaknesses of the undead, being one herself and her body would probably be too weak due to her sleep deprivation. She had her axe bass as her weapon. There was a point in the battle where Finn and Marceline found themselves back to back destroying the undead with the fury of 1000 party gods. At the end of the battle they all looked around at each other at the piles of undead that just lied there in pieces and started to laugh. Finn and Jake were battered and beaten from the battle because they had been fighting and running most of the day. But Marceline looked as she did before she even called Finn. Like a mess.
So, That's the first chapter. I'm going to post the second one right now just because this one is short. But feel free to comment on anything that might help shape the story, or just to criticize.