Note: Constructive criticism is welcome.
It was a dumb mistake that he got lost in Varia headquarters, and a chance happening that Belphegor was the one to find him, but Tsuna was sure that it wasn't an accident that they ended up in Belphegor's room.
"Your room's, um, it's very-" frilly "-nice, Belphegor-san, but I have to get to that meeting. Are you sure you couldn't show me the way? The right way, this time?"
"Of course I could," Belphegor said, rolling over on the enormous four-poster bed in the centre of the room and tumbling into a stack of pillows. His hair was longer than it had been at the time of the scramble matches for the rings, and he was turning it into a complete haystack. Not that Tsuna was in a position to judge. "But I wouldn't much like to do it!"
He looked terribly pleased with himself. "All right," Tsuna sighed. "I'll find my way..." He turned to leave but arrested the movement when Belphegor sat up, all teeth. That grin of his had a captivating quality, because you couldn't believe the top of his head didn't come unhinged.
"You're that relaxed about showing me your back?" Belphegor said.
Tsuna took a deep breath. He'd been waiting for something like this to happen since stepping foot in the Varia stronghold. He turned to face Belphegor fully, and that split second of movement was long enough for Belphegor to give him a face-full of metal - almost, if Tsuna hadn't dodged half by extending his turn in reflex and half by his knees giving way.
He didn't have time to berate himself for that bit of uselessness, scrabbling for a Dying Will pill and his mittens. He rolled along the ground, popping the pill into his mouth as he dodged a flock of knives, and then the prince himself was on him, knives held between his fingers to give him claws. Tsuna crossed his arms over his neck and blasted fire into Belphegor's face.
Belphegor howled and staggered back from him. Tsuna froze at the shrill, agonised sound and had to force himself onto his feet to watch Belphegor.
He was only singed, not seriously hurt. The attack had been too sudden for the dying will flame to build up heat properly, as it gathered together the ends of Tsuna's resolve. The realisation left Tsuna on the edge of relief; then Belphegor shook his head and hurled his body around like an acrobat, sending yet more knives soaring, and Tsuna felt only weariness because the fight wasn't over.
Belphegor laughed. "That was a good move! You'll get the hang of the family business yet!"
Not like that reverberated somewhere inside Tsuna, but all he could do for now was bite his lip and send more fire for Belphegor to dodge like he was dancing. Tsuna watched how Belphegor worked extra ducks and spins into his movements for what looked like no reason, shot another blast at him for good measure, and then worked his Dying Will flame up to the hottest temperature yet and fired a line of it through the room. Nearly invisible razor-wire fell slack from where Belphegor had pinned it, hissing and whipping, and Tsuna used more flame to burn away the loose ends that threatened to cut them.
"Aaa~ww!" Belphegor turned his face to the white-hot line of fire shimmering above him. With a desultory wave of his hands he shrugged his knives away, dropping them on the floor in a cutlery clatter, and Tsuna let his shields go out in surprise.
"We could have had so much more fun if you let me get even a little cut," Belphegor said, pouting. He wiped his face with the back of his hand, brushing off ash to reveal skin that was pink with heat. "Humph. Got me all heated up for nothing."
"Fun?" Tsuna said, his tone cold. "Fun?" he shrilled, and the flame flickered. He tightened his focus and stayed wary.
"You don't see it like that, do you?" Belphegor walked up to him, using one knife to cut the wires attached to his body, and then he flicked the knife away. Without looking, he got it to stick in one of his bedposts.
I won't give way, Tsuna decided, and wondered where that had come from. Did he really care about impressing a crazy assassin? Had Reborn and this life had such of an effect on him? Changed him so much? But he stayed where he was as Belphegor reached him.
"Fighting makes you look so sad." He carefully didn't flinch when Belphegor's hand raised because there was nothing in it, but he did flinch when one finger traced the corner of his mouth where his frown cut the deepest. "You're weird," Belphegor observed.
Then that jaw-cracking smile of his broke out. "You're going to be such fun, Vongola King. It'll be interesting with you around!" He put an elbow on Tsuna's shoulder, languidly leaning in. "I could never know what I'll see in your face."
The resolve not to give ground was tempered with flame, and Tsuna stayed still though his muscles shuddered with strain, staring back.
Belphegor's mouth made a slack little gap of incomprehension and enchantment, studying him like a page of a book. "I really will have to see more of you," he said, so close that their noses brushed.
"What the—Belphegor-san!" Tsuna sucked in air to make up for holding his breath and staggered back, the flame finally snuffing itself out.
"Vongola King! It wouldn't do to keep your subjects waiting. For one thing, Boss will kill you for it!" Belphegor marched up to him - Tsuna froze like a prey animal - and went past, stopping at the doorway. "Shall I show you to the conference room?"
Tsuna waited for the trick. Whatever his expression was made Belphegor look even more pleased, and he tried to make his face blank as he walked out of the room.
"Showing your back again," Belphegor murmured, but Tsuna made sure to do nothing more than flex his gloved hands. Belphegor gave an appreciative snicker and moved ahead to lead the way. He walked backwards, never bumping into anything or losing his way as he kept looking at Tsuna.
The meeting began on time, because Tsuna had been trying to arrive early when he wandered out of his room and into the rest of the building. He'd wanted to steel himself for the negotiations, but now he hardly had the attention to spare to be scared of Xanxus with Belphegor sitting there grinning.
All through that day and the rest of his stay Tsuna felt the stare and the fascination: when walking down corridors, across the table at meals ... in quiet corners in the gardens. When he went for a walk in town. When everyone else went quiet and looked between the two of them. Up against the wall where it was cold against his back and Belphegor was hot against him.
"Belphegor-san," he said, realising something, and Belphegor tried to bite him. He tightened his fist in Belphegor's haystack hair with an instinctive jerk, and the other boy whined like a kicked dog, like a pleased lover. Tsuna didn't even know if he should apologise. "I never know what to think of you either."
"Why are you talking?" Belphegor hissed in righteous confusion and shut him up with teeth and tongue and a stupidly skillful grind of hips.
Tsuna thought about how his scheduled stay ended today. He would go home in the afternoon and far away from this. He went nearly weak with relief, and then dragged Belphegor close, as close as he possibly could.