Disclaimer: Adventure Time belongs to Pendleton Ward/Cartoon Network.

A/N: This was unbeta'd, so apologies for any grammar errors. It was also supposed to be a prologue for Bubbline, but it got out of hand.


996 Years Ago

The huge shape towered over the two travellers, its humped shadow stretching out across the rolling grassland ahead of them. Marcy's hand tightened in Simon's as she looked up at it suspiciously, her other arm tightening around Hambo.

"What IS it, Simon?" she asked nervously, half expecting it to rise from the ground and come towards them, but the man beside her only chuckled gently.

"It's okay Marcy, it's just a tree. Looks like a big old oak or something." He squeezed her hand reassuringly, but still kept a careful watch for anything moving in the branches. He didn't realise his free hand was reaching for the crown at his belt until he felt cool metal against his cold fingers.

"But why is it so big?" Marcy still sounded suspicious. "None of the other trees are so big, or so green, and it's all by itself out here. Where are all the other trees?"

"It looks like these fields were farmland before the war," Simon explained, pointing at a row of rotted fenceposts. "For sheep or cows maybe. The farmer would have left the tree for the animals to shelter under in bad weather. And the bombs were aimed at the cities; they wouldn't have cared about the farms." As he spoke, Simon felt his confidence rising. If the bombs hadn't hit here, maybe there wouldn't be any mutants around. "You want to go have a look?"

"Okay!" Comforted by Simon's assurance, but still holding his hand tightly, Marcy followed him towards the giant tree, the grass beneath her feet a welcome change from the dry soil or broken concrete she was used to. After the near-disastrous trip into the ruined city to find chicken soup, Simon had decided that they should try to keep away from the formerly-urban areas and Marcy had seen more green things in the last three weeks than she had in her entire life. Even better, Simon hadn't needed to wear the horrible crown either.

As they got closer Simon realised that the tree was a willow, not an oak, which meant no acorns. But given the amount of greenery in the area there could be animals, maybe wild fruit or vegetables they could eat, and the tree's thick canopy would provide shelter. From its sheer size, at least fifty feet, he guessed that it was a couple of decades old, which was strangely comforting. The tree must have survived the war, just like them. Its trunk was lumpy and gnarled, and had branched off in places to form separate crowns, but its leaves were vibrant green.

"This old fellow would be perfect for a tree fort," Simon mused with a nostalgic smile, patting the bark. "I remember I used to have one when I was your age, Marcy."

"What's a tree fort?" the little girl asked, shading her eyes with one hand as she squinted up at the treetop.

Looking down at her, Simon was reminded once again of just how strange it must be for a little girl growing up in this world. He remembered the time they had found an old playground that had somehow escaped complete ruin and he had jumped laughing onto one of the swings only to see that Marceline was watching him in utter bewilderment. She hadn't understood what the metal and wooden things were for until he'd sat her on one of the swings and pushed her. Once she'd gotten the hang of it she hadn't wanted to leave.

"Well, a tree fort is like a house in a tree," he began. "For children to play in, I remember that mine had a rope swing and a ladder I could pull up behind me so nobody could get in unless they were a good climber..."

"I'm a good climber!" Marcy exclaimed. "I bet I could climb right to the top of this tree." Letting go of Simon's hand, she tied Hambo's arms around her neck to free her arms and started to scramble upwards.

"Don't go too high," Simon warned her. "I don't want you climbing any higher than that branch," he added, pointing at first split in the tree's main trunk. He was considering climbing it himself, though you could just fly up the crown whispered, there were plenty of foot- and handholds in the rough bark and it would give him a good view of the surrounding area. Keeping one eye on Marcy, he started to edge around the tree, looking for any edible fungus, then halted as he was confronted by a yawning split in the bark, almost the size of a doorway, which opened into darkness.

"Marcy, come down!" he ordered urgently as he backed away, dreading to think what might be inside that wooden cavern. Again, he felt cold metal and faceted gems against his fingertips before he even thought of the crown, but the crown was thinking of him, always.

"But I found a big hole!" the little girl called back, and Simon looked up to see her perched in the split of the trunk, pointing at another dark hole leading into the main trunk. "It looks like it goes right into the... Yeek!" Losing her balance, Marcy's flailing hand missed the trunk and disappeared into the hole, and the rest of her followed, vanishing into the tree.

"Marceline!" Without a second thought, Simon dropped his pack and darted into the hole in the main trunk, hoping it connected to the one Marceline had fallen into. Bracing himself to push his way through rotted wood, to Simon's surprise the only barriers he encountered were a few cobwebs. The hole opened up into a hollow chamber within the tree that was easily big enough for him to stand in. He tensed at the sound of scuffling, but then heard Marcy's voice.

"I'm okay! I think I'm in the tree..." Simon could hear her clearly, which suggested that they were in the same hollow chamber.

"That's okay, so am I..." he replied with a slightly hysterical laugh of relief as the mental image of the little girl's broken body faded. "Are you hurt?" Groping blindly towards where he thought he'd heard her, he felt a small hand take his. Somehow Marcy could always find her way in the dark.

"I think I got a splinter, but Hambo's leg got torn..." Marcy replied mournfully. "Can you fix him?"

"Of course I can, sweetheart." Simon said as he headed back towards the hole he'd come through. "This might be a good place to camp for a few days, it's lucky you found it." Since he'd been ready to run at the sight of the hole in the tree, Simon was willing to give Marceline all the credit.

"Is it a tree fort?" she asked, blinking as she stepped back out into the sunlight with Hambo clasped protectively to her chest, stuffing spilling from a ragged tear in the toy.

Simon was about to say no, then reconsidered. It wasn't like they were likely to find a real tree fort after all. "It is now," he replied, looking down at her with a smile.

o.o.o.o.o

Watching the campfire from a safe distance, because being too near its warmth made his skin itch like crazy, Simon reflected that this must be one of the strangest places they'd ever stayed, not least because they had started a fire inside a tree. He'd been careful to line the fire pit with rocks and keep it a safe distance from the tree's hollow trunk, explaining everything he was doing to Marceline as he always did. She'd need to know all these things if he ever had to wear the crown and didn't... come back.

The little girl was curled up in the sleeping bag a safe distance from the fire, Hambo clutched tightly in one arm with his leg repaired. They'd found a pond a short distance from the tree and managed to catch some fish for supper. This time Marcy had managed to catch as many as Simon, the ones they hadn't eaten were drying and smoking over the fire. She was a quick learner, which was reassuring, if Simon ever did lose himself she would be able to go on without him. Of course, he hoped that would never happen, but he'd also hoped that the war would end before either side resorted to atomic weapons. And look how that had turned out.

Shaking off those depressing thoughts that would inevitably lead back to Betty and the crown, Simon looked around the tree's interior instead. He still had no idea how it was even alive, the hollow chamber inside its trunk was huge and didn't look natural, as if someone had carved it out. Beneath the thick layer of dust and soil on the ground he'd found the remains of crude floorboards and wondered if this had been a makeshift barn or storehouse or something. There were no signs of recent habitation, so he had guessed that whoever had hollowed the tree must have done so before the war.

Whatever the reason, it certainly made a good camping spot, sheltered from the weather and it would be well hidden once the fire was out. Simon had blocked up the entrance hole with a spare blanket, and if he sewed bark to that then it would be difficult to notice at a distance. He hadn't covered the hole that Marcy had fallen through, it was too small for anyone that was larger than she was and also made a natural flue for the campfire smoke. If he rigged up an awning for it, that would keep the rain out.

The only sounds Simon could hear were the soft creak of the tree's timbers and the rustle of its leaves. Maybe they really were too far from the city for the mutants, if they'd been sleeping there then he'd have spent most of the night on edge, every rattle of shattered concrete a potential enemy, every sigh of the wind could be a mutant's groan.

Simon decided that he'd have a better look around in the morning, see if he could find running water nearby. If they were lucky there would be enough resources here for them to stay. Marcy needed some stability in her life after all. He could even make her a tree swing. Feeling happier than he had in a long time, Simon leaned back against the tree and went to sleep.

o.o.o.o.o

"Simon! Simon!" He woke up from a dream where the strange pink goo from the city had formed itself into Betty to find Marceline shaking him, looking worried. "Something's wrong!"

The memory of the dream faded as Simon blinked sleepily and put his glasses on, taking Marcy's hand as he stood up. "Is there something out there?" he asked, wondering if the tree did have an inhabitant after all. Oh glob, maybe it was a bear...

"No, it's the tree," Marcy replied, tugging at his hand to lead him outside. "Some of the leaves changed colour. It's weird!"

The two of them stepped outside and turned to look up at the tree. As Marceline had said, wide swathes of the leaves had turned varying shades of red and gold and were slowly falling to the ground. Simon had no idea how the seasons had been affected by the fallout from the bombs, if there even were seasons any more, but he could make it winter right now the crown whispered, but the tree looked like it was entering autumn.

"Don't worry Marcy," Simon told her, starting to walk around the tree to see how many of the leaves had changed. One side was still bright, vibrant green, which was odd. "Before the war lots of trees did this every year, in autumn the leaves changed colour and by winter they'd all fall off then grow back in spring."

"Like that?" Marcy asked, pointing ahead. Looking that way, Simon drew in a sharp, shocked breath. It was like winter had drawn an icy cold hand vertically down one side of the tree, the autumn leaves vanishing abruptly and leaving only naked, jagged branches. Even the bark looked different, darker and duller, and when Simon touched it, it was cold.

"That's not right..." he said softly, frowning. A horrible suspicion was creeping into his mind, and when he mentally mapped out the tree's interior in relation to where he'd been sleeping he felt a dull, sinking realisation. "It was me."

Marcy frowned as she looked up at him. "What was you? You never wore it," and both of them knew what 'it' was, "...so how could it be you?"

Simon had taken a few steps back from the tree, looking up at it regretfully. "That's where I was sleeping," he explained, pointing at the trunk below the leafless branches. "And the crown's already... changed me, so me being inside the tree harms it." He sighed heavily as he went on. "If we stay here, it'll die."

"So?" Marcy demanded, though not without a remorseful glance towards the willow. "Maybe it's the crown, you could throw it away or bury it or something, maybe it's not you!"

"I know it's me," Simon said sadly, because without a conduit the crown would be inert, it was part of him now, it loved him, it would never let go. "And I can't get rid of it, you know that Marcy, I need it to protect us." More than that, Simon was sure that if he did part with the crown then whatever power that had allowed him to survive the bombs when everyone else had burned and died or worse would vanish as well, and he'd die like they had done. Like Betty had done. And Marceline would be alone.

"Well... so what if the tree dies?" Marcy had folded her arms stubbornly. "We could still live in it, couldn't we?"

Simon didn't reply at first, looking at the tree instead as he continued to walk around it. Bare branches gave way to dying autumn leaves, but as he went further the leaves became green and healthy again. It took a few minutes for him to complete his circuit around the willow with Marcy following behind him and to his relief most of the tree was unaffected. Only the area that had been near him had been damaged by cold, though if they stayed here...

"It would be wrong, Marcy." Simon said quietly. "This tree's lived a long time, it survived the war, it could even be older than me. It wouldn't be fair to kill it."

"I guess," Marcy's voice was disappointed, but accepting. "And it would be mean to the animals that live there. It's still butt though."

"That's my girl," Simon patted her shoulder with a smile. "Come on, let's go get our things."

o.o.o.o.o

Half an hour later they had packed everything up and were ready to head onwards. Both of them had turned back to look at the tree one last time, hand in hand. Although he was hiding it well, Simon felt deeply uneasy. Would he kill all plant life he was near now? Would it start affecting animals? God forbid, would it affect Marceline?

"Marcy?" He kept his tone deceptively light. "You should remember where this place is, okay? It would be a good place to stay and if I'm ever gone..."

"Why would you be gone?!" The girl cut him off before he could continue, looking up at him with wide, frightened eyes as her hand tightened around his. "You're not going to leave, are you Simon?"

"No, no, of course not," he said soothingly. "But... I won't be around forever, and I'm way, way older than you." And one day you'll give all this up for the beauty of the ice and snow the crown whispered. When you won't even remember her name. "You understand, don't you?" Simon squeezed her hand gently, remembering how he'd found her wandering the city ruins as a toddler. She'd looked just as frightened then as she did now, but now she hugged Hambo close to her chest as her expression grew serious.

"I understand Simon," Marcy replied, nodding. "But that's not going to be for a long, long time, is it?" she added quickly.

"Of course not," he reassured her. You liar, the crown hissed. "Not for a long time."

"Good." Marcy said, as they turned away and started walking. "When I'm big I'll protect both of us, then we can stay wherever we want, and we'll never have to worry about monsters again."

Simon laughed in response, but the sound was fond, not mocking. "I believe you sweetheart. I know you will."