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The forest is as much of a living, breathing being as the creatures that live in it.
This is one of the first things that Katsuki learned in his life. His little hands grazed against the scratchy bark of great millennium-old trees, always so weak compared to the root system that he stumbled over just to get there.
Now, his hand is still small in comparison, but strong enough to protect it should he have to.
"I'm off, Kacchan!"
Katsuki glances up from the garden, the sleeves of his kimono rolled up to his shoulders. The sun is dancing through the leaves of the forest that surrounds the small house, and bursts of colorful light paint Izuku's skin as he pauses by the garden gate. Sun-catches make rainbows twinkle across his skin, overshadowing the happy smile he gives Katsuki. Just barely.
"Yeah, yeah. Get out of here already. If you're late, don't expect me not to eat your lunch."
Izuku's laugh is like the bubbling water of a river. Katsuki bares his teeth at him, but Izuku knows it's playful.
He leaves with a jovial wave of his arm, dressed only in the haori that Katsuki had tucked around his shoulders the night prior when he was lost in thought, staring at the fire. He does that often when the sun goes down, seemingly lost without the sun to guide him.
But, forever and always, Katsuki will take care of him.
Katsuki watches him go until he disappears between the shadows of tree trunks and bushes. Then he settles back down onto his knees in the garden, sprinkling water across the flowering tomato plants and carrot seeds.
Izuku is the forest spirit, tasked with protecting this and the surrounding nature of this island. He's gone off today, further than usual, to attend to the rumors of magic poaching and hunting on these sacred lands. It isn't often humans make it this far into the wild, no matter what fancy weapons they've invented, but it seems that the forest can't protect itself this time.
So it's up to Izuku to tend to it. His fate, or whatever.
Katsuki wipes sweat from his brow and stands, letting his watering can knock against his knees as he totes it towards the modest well that Izuku had enchanted for him. Always runs fresh and pumps easily, even in the winter when the ground frosts over. Katsuki sets the can there and leaves it to instead step inside, to get changed into something clean for the day.
Katsuki himself is… a shaman, maybe? A monk?? He's never really been able to label what it is he does now.
But he is human. A human living with a forest spirit, taking care of the land when Izuku is in his… less corporeal form. Maybe a week out of the month Katsuki is able to see his human-esque freckles and his wide palms.
They spend days and nights together until Izuku has to attend to the more 'spirit'-based aspect of his duties. Ones that mean he has to transform and roam the earth for a little while. Katsuki doesn't mind when he's gone. He gets plenty done, especially now that he's starting to learn magic from Izuku.
But it's when Izuku comes back that the ache in his heart reminds him how much he misses that dopey little smile Izuku saves for him.
"Tch."
Katsuki gets started on lunch.
---
As lunch cooks, something simmering at a low heat on the stove, Katsuki goes to bless the various shrines around the island. They used to be well cared for when humans were allowed here, but Katsuki is the only human now. He studied well on how best to honor the magic here, and carries with him a few incense and offerings to thank the other gods for always taking care of the land (and Deku).
The shrine closest to their home is one of the smallest, but no less honored.
Katsuki cleans it first, brushing dead leaves from the stone structure. It's discolored from years of sun and the elements toying with it, and Katsuki brushes his fingers against a few grooves that have been worn into its base. He'll maybe have to repair it by next year, but oh well.
Katsuki slides to his knees, lighting the incense with his fingertips. Something small he does every once in a while to practice his magic. The scent blends in with the peeled fruit that Katsuki arranges on a small plate, and the smoke runs off the flying bugs that might curiously try to steal bites. He sends a prayer and bows briefly.
It's as he's standing up straight that he feels something shift on the wind.
Katsuki's head lifts and the breeze picks up his sleeves, as if trying to tug him in the opposite direction. As if it's running from something. His ears tingle as he tries to listen beyond the sound of scampering rabbits and rustling leaves.
"Deku…"
---
"Deku!"
The sky grows overcast as Katsuki runs through the forest. Fallen leaves shuffle and dance at his feet, and he nearly trips over a rotting log. He loses a shoe in the stumble, but it's nothing that can't be replaced. He forces his legs to move faster, ignoring the bite of pain from pinecones and acorns digging into his soles.
"Deku!" He shouts. "Fuckin' answer me!"
In the distance, slow thunder meanders through the clouds. The sound trembles through the air, and Katsuki can smell the sharp, earthy scent of petrichor begin to bloom.
His destination is the middle of the forest. Even without Izuku's annoying voice calling, "Here, Kacchan!" he can feel the idiot in that direction.
Izuku lovingly dubbed it the Mother tree. It's the oldest one in this entire forest, tall and strong. Its roots are sometimes the only things that keep the other trees from succumbing to famine when the winters are too harsh and long. It's almost as old as Izuku himself is, for someone who has been alive… well, forever.
And it was being attacked, for some reason. Now that he's closer, Katsuki can hear it dying.
As he learns magic, he's grown more attuned to the forest. Every morning, just as the sun rises, he can feel the excited burst of magic that pops from Izuku as soon as his connection to the forest strengthens.
It sometimes wakes Katsuki up, but it's never an unpleasant feeling. Nothing like this.
It's as if his brain gets dipped in slimy sludge, black and inky and thick like curdled blood. It makes his stomach flip as if he's been thrown in the air and there's no ground to catch him. Katsuki isn't sure if the ache in his lungs is from how hard he's running or if it's attached to the feeling of his heart breaking in his chest. The tree wails for help, and Katsuki fears just for a moment that he won't be able to answer its call.
He bursts through the treeline in a heap, skidding to a stop as old branches shake themselves loose from his hair.
What greets him is… horrifying.
A group of humans surround the tree. Not too many, about four or five of them. They each carry chain-linked weapons that look like small scythes, and shiny crossbows that glint angrily in the sun. Izuku is between them and Mother Tree, transformed into a beast that Katsuki has only seen twice, in the distance after Izuku leaves him for the month. He's taller than the tree is, but hunched over as he tries to protect its trunk as the humans let loose a horde of arrows. It seems they've been doing it for a while, and Izuku's amorphous body has been forced to absorb them all.
When they impact, the skin goes from translucent to milky black and grey. Poisoned? Must be laced with something anti-magic at the least, because Izuku is rarely hurt from anything.
The wounds he sports he usually adopts consensually, to heal the trees that he was created to protect. His arms are lined with scars like the rings of a tree trunk, and Katsuki sometimes jokes that it's his true age. Izuku always laughs.
He doesn't want to think of how many more new scars will appear after this. The arrows seem never-ending. They halt, maybe, as the humans reload with even more in their packs.
"Izuku!"
The forest grows silent as his presence is acknowledged by the humans, by Deku, by the gods above, and even by the Mother Tree. The sound of nature has all but died out, too frightened to offer him strength even with the sound of birdsong.
One of the humans lifts their bow to aim it at him, and Izuku's monstrous form crushes them before they even move their finger towards the trigger.
Katsuki dodges anyway, following the edge of the treeline. He weaves in and out of it as more and more of the arrows turn to him, the cacophony of human language mixing with the twang of bowstrings. Katsuki doesn't know the language, but he can tell that they're pissed. A few of them are already dead, it seems, by Izuku's hand.
Izuku, frankly, doesn't look much better.
His spirit is… hollowed out. It looks as if his chest is invisible, the strength being sapped out of him the longer it takes to win this battle. He keeps reaching his hand up to the sun for strength, but the clouds are working against them today.
The sun, Izuku's strength, has hidden itself behind them.
Katsuki reaches for his magic and sends a flare of light outward, blinding everyone in the area. Even Izuku cries out as his vision is accosted by the unyielding burn. Katsuki uses the confusion to his advantage and, by the time the humans have recovered, ends up stealing four of the crossbows right from their grasp.
He burns them with his magic, and gags at the acrid scent of poison mingling with it.
Ash clings to his hakama, staining the already dark fibres. Katsuki glances away from it just in time to watch how the humans try to rush him from all sides, abandoning the weakened forest spirit for the moment.
Katsuki darts back to the treeline again for safety, but he nearly gets caught by grabby human hands. It's with a snarl that he slaps them away, but one of them is able to yank on his sleeves and nearly tug him to the ground. He stumbles forward.
Izuku roars.
The ground waves like liquid water as Izuku's hand slams against it. A tree falls in the distance with the force of the attack, adding to the discord. Katsuki's sleeves are released as the humans cover their ears from the agony, but Katsuki is able to withstand it enough to retreat once more.
He scrambles against a tree just in time for Izuku's other hand to come down right upon the group.
Katsuki covers his ears with both hands, dropping low to withstand the second burst of sound. The screaming of the humans is nothing but a flap of butterfly wings compared to Izuku's rage. Katsuki squeezes his eyes shut as his stomach lurches, nauseous as another tree falls closer this time. Izuku will be so upset to learn he was the one who did it, but…
When the noise dies down, Katsuki peeks out from his hiding place. He grunts in pain when he realizes that one of the humans had been able to slice at him with a knife in the fray, but it was only on his forearm.
Only two of the humans survived the assault, but Izuku's out of energy.
Clutching his arm to quell the blood, Katsuki scrambles out before Izuku can panic and think that he had accidentally killed Katsuki, too.
"Here!" Katsuki shouts. "Come here!"
He opens his arms wide, even as the remaining humans scramble to regroup and find their weapons again. Familiar eyes stare at him, almost unseeingly. It's like looking into the moon and expecting to see your reflection back.
Still, there's no malice in that gaze as Izuku slowly lifts his hands to reach out for Katsuki.
Izuku comes to meet him, body shifting one limb at a time back to the form that Katsuki is well-acquainted with. The wounds look worse like this, and blood immediately begins to spill from the holes that the arrows made in his body.
Katsuki hisses as he reaches to catch him. Izuku falls in front of him, the entire ground shuddering with the weight of his body. It's like an earthquake, and Katsuki nearly loses his footing. He drops purposefully, hands gripping Izuku's shoulders to get him to move somewhere safe.
"What were you thinking?" Katsuki gripes immediately. "I could have helped, you should have come to get me."
"H-had to… had to save it." Izuku's voice is half human, half spirit.
Katsuki has never heard it aloud, but he's felt Izuku's spirit before in his heart. It's usually soft and light, if not a bit overbearing when he's excited. Now, it makes Katsuki's eyes prick with unshed tears.
"The tree can be replaced, Deku. Dammit. Not you— fuck!"
Katsuki gasps as an arrow shoots past him and embeds itself in bark. The humans have their weapons again.
Immediately, the poison seeps in and the tree's trunk grows sickly pale and fragile. When Katsuki reaches to touch it, Izuku's weak grip tightens.
"Don't."
His voice drags and slurs, as if he's drunk. But behind the tone lies a hint of pain.
Katsuki drops his hand and drags Izuku behind the tree as more arrows volley towards him.
"Stay here. Don't fucking move until I come back, I'll take care of the rest."
Izuku gasps in pain as Katsuki dumps him on the ground, carefully cradling his head until it lands against a bed of softer leaves.
Then he stands, fists balled and face red with anger. He can feel how his skin boils at the thought of these fucking nobodies trying to ruin a forest for… what— money? Because some stupid king somewhere wants to claim more land?
Fuck that.
Katsuki doesn't know much offensive magic, certainly much less than Izuku himself knows seeing as he is the one who taught him, but he's nothing if not innovative.
There will be one winner today, and Katsuki guarantees it'll be him.
---
Bodies line the forest floor.
Katsuki breathes heavily where he sits at the base of Mother Tree. There's a slow gush of blood dripping from a wound on his face, but otherwise he's unharmed.
Izuku is collapsed beside him, exhausted of almost all of his spirit. Of course he hadn't listened when Katsuki left him behind, but they'd won nonetheless. Katsuki's haori is wrapped around him to preserve his modesty and to keep him warm as soft rain begins to trickle down.
Most of the poison is purified, both from Izuku and the tree, but the tree will suffer for a few months more. Katsuki apologizes to it one last time, leaving behind an offering consisting of a lock of his hair, blood dripped from Izuku's finger tip, and the peeled apple that he was meant to leave at another shrine. Hopefully it'll be enough until Katsuki can come check on it again in a few days.
Izuku, though, needs his attention more.
"C'mere," he grunts. "You damned idiot."
When Katsuki was younger and he first met Izuku, he was horrified at how easily the forest spirit had disregarded his own pain for the sake of the forest. Sure, the forest deserved to live happily and in harmony with the world but… how could it do that if Izuku killed himself for its prosperity? Who would take care of it in his stead?
That damn worry wouldn't leave Katsuki even as he grew older and watched Izuku get more and more reckless. It took Katsuki angrily declaring that he would leave and never return for Izuku to stop giving up himself for every broken branch or lightning-struck tree that he came across.
Katsuki had researched remedies. He never thought he was the healing type but… he blamed Izuku. Now, though, he's grateful that he'd had the wherewithal to look up poison remedies too.
The taste of the medicine is… disgusting to say the least. So bitter that it feels like his tongue is dry. But he chews the dried herbs thoughtfully as he looks down at Izuku's exhausted face. His eyes are half-lidded as if he's dead, but his chest is slowly rising and falling. His magic is weak, but thrums tiredly when Katsuki reaches out for it.
Izuku's body tenses when Katsuki bends over to press their lips together, shifting the medicine from one mouth to the other.
A weak noise builds in Izuku's chest, but Katsuki clicks his tongue to shut him up as he takes another bite of the medicine.
"Swallow," he orders. "If you die here, I'll kill you."
Izuku doesn't respond, but his hand fists against the ground, gripping a handful of grass against his palm. Katsuki looks up at the sky as he chews more, and glares as the sun shyly peeks out to say hello again despite the rain.
When he looks down again, Izuku's face has gone from pained to relaxed. Even though blood drips from him like the rainwater from tree leaves, he looks at peace.
Katsuki lets the medicine mash against the backs of his teeth before he bends over to feed it to Izuku again.
---
Katsuki leaves behind the humans. Their bodies will decompose and feed the scavengers and bugs. Hopefully those nutrients will undo atleast a fraction of the pain they inflicted on the forest.
He has to carry Izuku on his back. He's heavy, and they have to pause often for Katsuki to catch his breath all over again. But Izuku doesn't wake the entire way home, even when Katsuki warily lays him down to give him one more helping of medicine, desperate in the way he grips Izuku's chin to open his mouth.
They make it home, eventually. The sun is setting and the sky grows pink like the inside of a pomegranate. The stars, just like the seeds.
Izuku wakes a few hours later, eyes popping open as if he hadn't closed them in the first place. Katsuki had laid him against the garden, to let some of the magic from it seek out the forest spirit himself and aid him in his recovery. Katsuki wasn't sure it was going to work, but Izuku had enchanted the soil there himself.
Katsuki had half a mind to bury him just to be spiteful, but he'd been too worried about his wounds.
Izuku sits up, groggy but alive. He's still wearing Katsuki's haori, though it's full of holes now. Katsuki can easily fix it. Not so much the dumbass who is wearing it.
Katsuki sighs wearily, and stands to walk back into the house. Izuku scrambles to catch him before he does, both hands wrapping around Katsuki's wrist.
"When I saw you appear, I was so worried they would kill you," Izuku begins, frantic. "I can protect the forest, but… humans are unpredictable. Frightening. You shouldn't have come."
Katsuki snarls. "You're lucky I was there. They almost got you and you're a god."
Izuku swallows thickly, guilty as he breaks eye contact. Katsuki sighs.
He offers his other hand out to help Izuku stand, and the forest spirit looks much better than he had a few hours prior. His pallor has grown less pale, and he doesn't look like he's about to disappear from sight. When he's at his full height, Katsuki knocks their foreheads together to look him in the eye again.
"You can't do that again, Izuku. I won't let you do that alone."
Hesitant arms wrap around him. Izuku smells exactly like the forest, but fresh like mint. Soft like honeysuckle. Katsuki wants to melt in his embrace as Izuku hugs him.
"It's my duty," Izuku says simply. "But I wish I hadn't worried you."
"You're training me to protect this forest too. You don't have to do it alone anymore, you shitty spirit."
Katsuki releases his breath in one quick sigh. It makes him deflate, and his eyes blink open again. "But, I get it."
Izuku flinches.
"… Are you going to tell me you're leaving?"
Katsuki snorts. "I fuckin' should. If you aren't going to let me help then what's the fucking point of me being here?"
Izuku goes stiff, his grip tightening on Katsuki as if the thought is unbearable. Katsuki grunts when that hold doesn't get released, and Izuku's frantic magic nips at his own spirit.
"I won't, Deku. Not after all of this."
Neither of their hearts would be able to take it, surely.
"But shit like this isn't going to happen again. You're going to teach me how to properly defend this forest this time. This forest and you, in case those shitty humans come back. Got it?"
Izuku nods, but Katsuki continues.
"I'm serious. Even if you don't know how to fight, then fucking find someone to teach you so you can teach me."
Izuku's lip curls into a wobbly smile. "You want me to teach you, no matter what?"
Katsuki has half a mind to punch him. Instead, he rolls his eyes and turns away. "Shut up."
For some reason, the sound of his dumbass forest spirit's laugh comforts him and has his shoulders relaxing. Just like that, the frightened twinge from Izuku's magic calms again, as if all he was scared of was losing Katsuki to something or someone.
Katsuki snorts. Who knew a forest spirit could be possessive of a human.
"Come inside to eat. Lunch is probably spoiled by now, so you better help me peel potatoes for dinner."
"Of course, Kacchan. Should I chop the onions, too?"
"Fuck no! You cry like a baby when you do."
The sound of Katsuki's fussing grows muffled as the two of them slip back into the house. In the morning, Katsuki will have to add a bit more soil and replace some of the garden vegetables that gave up their life energy so that Izuku could heal properly.
And afterwards, Katsuki will grow even more determined to take care of him. He'll see the new scars that have circled all the way up to Izuku's chest from the battle, and swear that not a single new one will appear— even if he has to fight Izuku himself to achieve it.
And, silently, wonder if it's okay that he fell in love with him. A human and a forest spirit…
Katsuki already knows Izuku feels the same, regardless.