Fionna crept close to the ground, walking basically right underneath the guard's noses. They were mostly yawning, both bored and tired. She almost wanted to teach them a lesson, hurt one of them to make them more alert, but she remembered that wasn't who she was. She didn't hurt people for no reason.
She leapt over a small hedge and began to climb a thick wall, brick by brick. It was extremely easy to climb, but every now and then she had to freeze to make sure she was invisible to the soldiers. She jumped over the side of the wall, and sprinted along its edge, her balance never wavering on the thin bricks. She jumped from the top of the wall onto a watch tower, which she climbed and perched on top of.
She scanned the scene. This one was much more familiar, being a main part of her childhood. She had come here almost every week when she was 13.
Now, even 7 years later, she still remembered everything. The taller of two large towers was where the Prince slept. She felt inside her cloak for the small letter she had prepared for him. She would not wake him like she had for Cake, she was simply delivering her greetings and a few interesting stories from her travels. She knew he would read the letter to Cake, so she had included special details that her sister would enjoy. She wished she was able to bring gifts, but even the small letter was dangerous to carry.
There were so many people she had made enemies with, there was no telling what they would do to her friends. Doing good always ended with something bad these days, she thought darkly.
She scaled the wall swiftly, jumping here and there until she was at the right window.
Peering in, she saw a dark form lying in the large bed. She tried the window, knowing it was locked, and pulled a tiny knife, as thin as a needle from out of her hair. She picked the lock, and within a matter of seconds she was standing beside the figure, about to take out the envelope.
But before she could the carpet beneath her seemed to swallow her up alive. She became entangled in it, the rug acting like a powerful net, closing in on her. Acting quickly, she pulled a larger knife from her boot and cut open the carpet in quick movement. She rolled out, and jumped to her feet, her knife in one hand. She used her other to reach behind her back, where her long sword always remained. She began pulling it out silently, when a razor sharp blade suddenly appeared beneath her chin.
"Don't move." Came a familiar voice from beside her. She couldn't understand how she had not seen the blade.
"Lower your hands, and drop the dagger." He commanded.
It was barely a knife, she thought, but dropped it anyways and raised her open hands peacefully.
"Now, you can go quietly and I can go back to sleep, or I can call the guards and put you in jail where you will be very uncomfortable until you eventually escape." Prince Gumball said, moving the blade even closer to Fionna's neck.
"I was planning on leaving quietly anyways, but I was going to give you a letter…." She said casually, smiling as the sword dropped. She could tell he was clearly expecting the Ice Queen.
"Fionna?" He asked in a shocked voice. She lowered her hands and reattached her knife to the boot before standing again and addressing him.
"How come I didn't notice the blade?" She asked curiously. She wanted to know before she left.
"Really? That's the first thing you say?" He asked, bemused.
"I know the lock must have been wired, or maybe a stone in the wall, but the blade is brand new to me." She said, picking up the thin sharp sword her had been holding.
"Very well, its my own design of course, made from glass. Very breakable, but easily deadly when used correctly." He said, taking it from her and weaving it in the air artistically.
So that's why she hadn't seen it, because it was glass. She thought interested. She pulled the letter out from the cloak and held it out for him. He seemed very much awake now anyways.
"So you weren't planning on saying hello yourself?" He asked, taking the letter and examining it.
"I already told Cake, my time is extremely limited. I actually need to be going now, still one more visit. And it's already almost 3am." She added, looking out the window at the clock. Time was flying tonight.
"But it's been-
"I know, I know, two years. But I really need to be quick Gumball." She said seriously.
"Cant you stay? Just this once? Please Fionna, just one day! Think about all the people who haven't seen you since you left all those years ago." He said pleadingly. She looked at him sadly. She had missed her friend, but she couldn't make any exceptions. When the sun rose she had to be far away, ensuring that the people who wanted her dead wouldn't hurt the people she loved instead. She shook her head. She glanced out the window again. 2:48am. It was time to go.
She was about to climb out the window when he grabbed her cloak. But it wasn't completely fastened from when Cake had been pulling on it, and it slipped off. Fionna grabbed for it, but it was too late. She already felt Gumball staring at her face.
"Your…..face." He whispered. She didn't look at him, she just pulled the cloak back around her shoulders and pulled the hood over her head, hiding the long scar that reached from her eyebrow to her cheekbone on the right side of her face. Her hair covered most of it anyways. She wasn't ashamed of it. To her it was just another battle story, a sign of bravery, a mark of victory that she was still alive but left with the wound. She turned again to the window.
"Wait, I'm sorry….I didn't mean anything." He said, grabbing her arm this time. She looked back at him.
"I know you didn't. It's ok Gumball." She said, giving him a quick smile and a small kiss on the cheek. She didn't mean anything by it, it was just a friendly goodbye. She had learned long ago to leave some feelings behind when you face death each day. This time she turned for the final time, and swan dived out the window.
She let the gush of wind pass her face, pulling a thicker dagger from her waist, thrust it into the side of the wall as she fell. The blade stuck into the stone, and she began to skid to a halt. Her feet touched the ground at the last second. Smiling to herself as she pulled the blade from the wall, she fastened it back to her belt. She took one last glance back, and gave a small wave in the direction of Gumball's window. She didn't know if he saw it, but she felt like doing it anyways. With the twirl of the thick cloak and the silent sound of her boots on the ground, she was gone. An invisible creature flying from place to place.

Prince Gumball watched from his window, his mind replaying the image of her face. In 20 years Fionna had grown to be the most beautiful thing he had ever seen, and the scar only added to it. It was a symbol of her bravery, her incredible courage for everything she did and risked. He touched his cheek where she had kissed him, wondering when he might see her again. He looked down at the thick envelope in his hands, the paper course and apparently hand made. He opened it.

Dear Prince Gumball,
I will assume you will share this letter with Cake, and so I write my undying love for her, and my longing to be with her again. Please make sure she knows she is always in my mind and I miss her more than I can tell.
I wish I could offer gifts of my travels to the both of you, but unfortunately it is for your own safety that you do not know where I have been. But I do have many wonderful stories to tell you.
The first real adventure I encountered was when I cam across mountains higher than anything in even the Ice Kingdom, and climbed them to the top. The air was so hard to breath I thought I wouldn't make it down, and upon my luck I found a dragon's den! After fighting to control it I managed to make my way down the mountain on it, but it took me much further than I intended. After escaping the fate of becoming its dinner, I found myself in the most glorious woods. The trees I saw there weren't even trees, but enormous flowers! The leaves were so big I made a shelter from them, and stayed there quite peacefully.
Many stories later, I found a place I think Cake would have enjoyed immensely. It was a place where the moment you passed into its territory you became your spirit animal. I won't tell you what animal I became, rather you must guess and imagine, and perhaps someday I will tell you. It was really very amazing though to walk around and converse with all these people who had been turned into animals, and truly showed the traits of what animals they were. I spent a good deal of time there, helping out with mysteries and crimes that had before been unsolved. All the time I imagined if Cake would actually turn into a different animal, or if she would turn in to a human herself! I also thought about what animal you would be Prince Gumball, but had absolutely no idea. I assume something pink, but there are very few pink animals. I happened to meet a book shop owner who was a goat, and he was very intelligent, but I find it hard to imagine you as a goat, especially with their little beards.
It was very difficult getting out though, because I had no idea how to return to my original form. Eventually I learned that by finding the animal that your spirit animal takes the form of, and giving it an offering it accepts with respect you may return to your original state. Again, I won't tell you what my animal was, but I will say it was rather difficult to do this.
I'm afraid I am running out of paper, and there are no suitable materials around to make more at the moment. Ink is very low as well, because the poison berries I am using are almost gone, and I'm in a very strange dessert at the moment.
Your friend,
Fionna

Gumball read it over several times, smiling at every part. He wondered what animal she was, and what animal he would be. He imagined her animal to be powerful, but also gentle and beautiful. Perhaps a stallion, with a long white mane. Or maybe something smaller, that you wouldn't expect to be dangerous, like a fox.
The clock struck 3am, chiming and awakening him from his thoughts. He put the letter down on his desk, folding it neatly and went back to bed. But he did not fall asleep.
He couldn't stop thinking about Fionna long enough to even shut his eyes.