Takuya just barely makes it onto one of the trains. He doesn't know where it's taking him, but he knows, down in his bones, that he needs to be on the train. The calm, almost boredom coming from the other two teens on the train gives him the impression they don't feel the same, and the little bawling kid clearly feels more fear than destiny coursing through him.

None of them realized what they would go through would leave its mark on them, both internal and external.

oOo

Takuya becomes a being of ones and zeros and the epitome of fire.

It's exhilarating, an energy surging through him that is unfamiliar but powerful and it is him, this energy and him are indistinguishable from each other.

The feeling is over all too soon. Takuya only has half an idea of what has just happened, the absolute thrill and adrenaline having fueled him up to this point. One minute he's tall and strong (so strong, so powerful, and there's a second heartbeat alongside his in his chest and he feels like there's somebody grinning at him, somebody who has been lonely for far too long) and then the world blurs in ribbons of data and he's back to being Takuya-sized and flesh and blood. The kid - Tommy? Yeah, Tommy, that was his name - was still staring up at Takuya with starry-eyes and the slight gleam of his earlier tears. He was holding onto JP's clothes, little fingers gripping the fabric tightly as if still afraid of falling into the chasm only a little ways away. JP looked speechless, jaw gaping open without a word coming out. Zoe too looked impressed, making sure to keep her distance from the edge, and looking all over at the damage that Takuya had caused during the fight.

The two weird monster things (they called themselves… digimon? Was that right?) mostly just look satisfied and relieved with the turn of events.

And Takuya himself, as the adrenaline drains away, mostly feels tired and sore.

He falls right on his butt with an ungraceful 'oof', rubbing at his shoulders. After being so filled with energy just moments ago, he feels so completely drained now and absolutely starving . There are sharp pains on the side of his head, his jaw aches and the middle of his back is far too hot, like the fire that had danced so harmlessly across his fists had settled as a burning coal onto the center of his spine. He arches his back slightly in an effort to keep his shirt from touching the tender spot.

"Hey, you okay?" JP is on him in a moment. Apparently nothing quite breaks the ice between people like being attacked by a monster and then saving the others by becoming a monster.

"Yeah, yeah just give me a second." Takuya grunts, lying down stomach-first on the cold ground. It's nice on his skin, which is now just a bit too hot to be considered comfortable. "Hey, does that book say anything about what happens after you use the armor stuff?"

"Oh, uh," The digimon pulls out his book, flipping through it, "No, it mentions nothing about any after effects."

"Great." Takuya groans. "Does it at least tell you what the heck just happened to me at all?"

"That would be digivolution." The digimon says, as if it's extremely obvious and he had no idea how Takuya hadn't known. Takuya regards the D-Tector in his hand.

"Digivolution, huh?"

oOo

Before they start off following the tracks, they stop by a river. Bokomon goes over the importance of travelling on a full stomach and drinking water when they can. Nothing is ever stable on a journey. Takuya goes a little ways off from the group and takes off his shoes, sinking his feet and legs into the cool water, and then his arms too. The heat had gotten worse the second time he'd tried to digivolve, as well as the various pains throughout his body.

"Alright, we can't dawdle. The Forest Station is very far away." Bokomon says and Takuya groans, pulling his feet out of the river and kicking them around in an effort to try them off before putting his shoes and socks back on.

"You okay dude?" JP asks. He and Tommy had splashed around during their break and both are still pretty wet. Takuya shrugs.

"Mostly just sore. I guess digivolving really can take it out of you." Takuya stretches out, and the action helps to loosen some of the tightness in his muscles. The center of his back still feels raw, and he flinches as his shirt brushes against it. "I don't suppose you carry around some bandages or something on top of all that chocolate."

"Did you get hurt?" Tommy asked, pure worry in his huge eyes. He looks like he might start crying around. It's weird how different the kid is from Takuya's own little brother, who has the same hard-headedness as Takuya and rarely ever seems to cry these days.

"Maybe?" Takuya hovers a hand over the spot on his back. "I can't really see it, but I think I might not be as fireproof as Agunimon as I thought I was."

"If you're burned, you should soak it in cold water." Zoe advises, approaching them from where she'd been a bit farther down stream.

"Yeah, I'm pretty sure that'd end with all my clothes soaking yet." Takuya points out. Zoe sighs and rolls her eyes.

"Give me your jacket."

"What?" Takuya narrows his eyes at Zoe and she just rolls hers again.

"Oh stop being such a baby. Give me your jacket." Cautiously, Takuya does just that. Zoe soaks it in the river water, bringing it out still dripping. "Now lift your shirt up and bend over. I'll drip some of the water onto the burn and hopefully it'll run right off."

Takuya stares down Zoe, trying to make sure that she was trying to pull something on him. He's grown up with a little brother, after all, and has learned to be a bit cautious. Zoe looks like she's about to start rolling her eyes again, though, so Takuya pull sof his shirt and bends over.

There's silence for a moment.

"Uh, Takuya, you didn't burn you back on purpose, did you?" JP asks. He had seemed bored, but now he's clearly interested in whatever is up with Takuya's back.

"Of course not! Why, what is it?" Takuya tries to crane around and look at his back, at the burn there, but isn't able to contort himself enough to get any kind of view of it.

"It's that symbol on your, uh, Agunimon's head and belt." Tommy explains. Takuya hasn't seen Agunimon as much as the others have, but he's seen the symbol appear on his D-Terminal, and remembers it from the armor earlier today when he'd first found the spirit.

Takuya lets Zoe drip cool water on the burn, and it both makes it sting and feel better as the heat is drawn out of it.

JP tells him not to worry, that it's about the size of his thumb. The area around the mark wasn't blistered or badly burnt. It was clean and precise.

Takuya has to stop himself over and over throughout the day from touching the burn himself, feeling out the lines.

oOo

The digivolution gets easier.

The more Takuya becomes Agunimon, the longer he can last before he gets tired, the less time he needs to rest and eat before being able to substantially digivolve again. The heat that accompanies the aftermath of the transformation becomes comfortable, and Takuya is unsure whether the heat gets better or he just gets used to it.

There's still a soreness that accompanies each. The sides of his head are killing, his shoulders feel like a hammer has been banged against them. His lower jaw is sensitive, making it unnecessarily hard to eat the food even though he's starving.

After the others get their spirits, they report different pains as well. Sometimes they match up, other times they don't. Bokomon and Neemon are both unable to supply any kind of answer, seeing as they were apparently the first humans to have used the spirits in this way. Each of them have a symbol in the center of their back. Takuya doesn't mention it, but he can feel the mark getting bigger, spreading a little farther with each transformation.

It's a couple weeks after they arrived in the digital world that the soreness reveals its purpose.

oOo

Takuya de-digivolves, becoming just Takuya once more, and doesn't fall down this time. He's proud of himself for the accomplishment, a true show that he's getting the hang of this whole thing, and he grins to himself and then directing the grin to his friends (by now they are his friends, his best friends in fact, and it makes him wonder how he ever really thought the small bonds he's had with other classmates were real friendships when compared to what he and the other digidestines have).

JP doesn't have the same stamina that Takuya has - it makes sense, considering he got his spirit last of the gang - and wobbles where he stands before sitting down, though it's clear he was going down one way or another.

"Takuya, what happened to your head?" JP says instead of any after-battle banter. Takuya blinks, taken by surprise by the question.

He touches the side of his head - the part that was always sore - and feels something jutting out from his skull.

"The hell?" Takuya's other hand flies to the opposite side of his head and finds the same thing there.

"What is it?" His distress has attracted the attention of Tommy and Zoe, who both stumble towards him, help up by the leftover adrenaline.

"Takuya has horns!" JP fills them in.

"I don't have horns!" Takuya shoots right back.

"Takuya has horns." JP insists again and gets back to his feet. Takuya keeps feeling the weird thing that are now on the side of his head. They're pretty short, maybe half the length of his finger, but they weren't there before he'd digivolved today.

"Your jacket is weird too." Zoe points out and Takuya realizes something.

The uncomfortable pressure in his shoulders, in his jaw, on the sides of his head, has lifted some.

Slowly, Takuya brushes a hand on his shoulder. There's a bump there that isn't supposed to be there, a little upward curve with a sharp end.

"Guys… I think I have an addition for Bokomon's book." Takuya says carefully. He runs his tongue over his bottom teeth. He isn't surprised when he finds his bottom canines bigger and sharper than they should be.

A/N: I hope to write more for this fic, but it'd require me to rewatch some of frontier, which I haven't actually watched for around... five? years? Maybe more? So forgive any errors, because I can't remember this that well. Also, if you think this is an interesting and cool idea, check out my other fic Binary in the Blood, featuring a similar premise but with the Adventure kids.