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I.
When Izuna saw Tobirama attack him with a somewhat wobbly lightning jutsu rather than his usual water, he was offended.
What the hell was that demon doing, attacking him with some unfinished jutsu? Granted, even an incomplete jutsu coming from Tobirama Senju was a grave threat, but still. Was he not fighting for his fucking life?
Izuna grunted as he narrowly avoided the precise lightning strike aimed towards him, and knew it was only because the Senju was not quite a master of the element that he was even able to do so without getting struck. Throughout all of the battles he’d participated in, Izuna had never seen such a jutsu, and knew it was likely something Tobirama had come up with on his own. Somehow.
Sharingan active, Izuna dodged another frighteningly quick attack from Tobirama and lunged for him in a counter-attack, managing to nick the man’s arm before having to pull back from another swipe of lightning. Up close, he could see how the lightning almost pooled at the Senju’s fingertips. It was as entrancing as it was frightening.
As the battle wore on, the lightning bent easier to Tobirama’s will, and by the time the Uchiha and Senju called for a retreat, Izuna found himself singed in various areas, his muscles twitching from the lightning Tobirama managed to shoot through his joints when he caught him. Madara and Hashirama may not strike to kill, but Izuna and Tobirama most certainly did.
Izuna smirked a little to himself as he limped back into the compound - Perhaps he’d finally backed the Senju Demon into a corner with his usual tactics.
II.
When the Uchiha and Senju met again on the battlefield, Izuna was even more confused when Tobirama still hadn’t brought back his usual water jutsu, opting instead for lightning once more. This time, however, the lightning seemed to skitter along Tobirama’s body, enhancing his movements even more and making his taijutsu frighteningly powerful. When the Senju managed to land a well-placed kick to Izuna’s chest, sending jolts of lightning through his body and causing his heart to stutter, he realized he’d need to be far more careful in his moves today.
Thankfully, Izuna wasn’t entirely reliant on his fire nature either, and managed to counter several of Tobirama’s lightning-enhanced attacks with wind. It wasn’t his nature of choice, and his jutsu paled in comparison to his natural fire ones, but it did the job in keeping Tobirama far enough away to stop him from landing another attack that most definitely would stop his heart.
This time, by the time the battle had ended, Tobirama had reverted back to his usual water-based attacks, and Izuna with his ever-active sharingan when in battle couldn’t help but notice how the Senju looked almost… frustrated? Not with Izuna, but with
himself
. He wanted to believe it was because Izuna had gotten the upper hand, and perhaps that was part of it, but he couldn’t help but feel like it had more to do with the way that lightning ability worked. Somehow, the thought of their very life-or-death fight taking a backseat to… what, some new jutsu practice? It pissed Izuna off.
III.
By the fifth or sixth time they clashed, Izuna had concluded that Tobirama was definitely using him to test out whatever thing he’d decided to come up with in the interim. It was infuriating - not just because Tobirama seemed to think Izuna weak enough to not bring his very best , but also because Izuna found he didn’t… really mind it. He’d taken a sort of sick fascination with anticipating what the Senju would attack him with next, and Izuna hated how much his sharingan seemed to eat up all the little useless details that had little to do with said experimental jutsu and more to do with how Tobirama’s face would scrunch up a bit when it didn’t react the way he wanted, or when Izuna could easily counter it. It was kind of cute.
Still, though. Infuriating. And Izuna wanted answers, so when the two clashed swords on the battlefield (Tobirama had brought some new blade coated with something that made his eyes burn and water), he couldn’t resist yelling at the man.
“What the fuck do you think you’re doing?!” Izuna barked in Tobirama’s face, and the Senju had the gall to look surprised in return.
“Trying to kill you.” He replied bluntly and Izuna resisted the urge to roll his eyes, solely for the fact that it would create a great opening to get stabbed.
“No!” Izuna yelled, grunting as their swords met once again in a standstill, “I mean why are you using all these new, weird elemental attacks and weapons!”
The two traded blows for another few moments before Tobirama replied.
“Well, how else am I going to fully test them?” He grunted as he dodged one of Izuna’s fireballs.
“Are you serious!” Izuna screamed. “Do you think I'm so weak that you can just bring your little experiments to the damn battlefield!?”
Clashing swords once again, Tobirama leaned in, his gaze so intense that it made Izuna’s heart nearly beat out of his chest.
“If you think I am doing this because you are weak, then you are far stupider than I could have ever imagined.” He growled softly and launched himself backwards in order to form several hand seals for his next attack.
The indignant screech that Izuna let out was loud enough to startle Madara from his own fight, looking at him with a mixture of concern and confusion.
IV.
By the time several months (and skirmishes) had passed, Izuna had come to terms with the fact that Tobirama would more likely than not bring something new to their fights. Despite the new normal that had settled, Izuna couldn’t help but be bothered with the fact that not only did he expect such things from the Senju, but actually looked forward to it, to the point of coming up with some new abilities of his own. He might not have quite the inventive mind that Tobirama had, but he knew how to stretch and improve what he already had.
Even more bizarrely, as their fights went on, Izuna realized that they had somehow gone from “try to kill each other no matter what” to “really aggressive sparring and/or experiments”. He certainly didn’t mean for things to wind up like that - whatever Tobirama crafted, Izuna would do his best to create a counter, and somewhere along the line he’d forgotten he was not just supposed to counter him, but overwhelm and kill him.
Whatever, it wasn’t like he was suddenly some bleeding heart that preached peace with the enemy the way he’d constantly hear Hashirama Senju cry out at Madara at every given moment. He still wanted to kill Tobirama. It just went a little lower on the priority list now. Nevermind the fact that his brain had oh-so-helpfully decided to move Tobirama from the “Monstrous Demon” category in his mind to “Weirdly Hot Rival”. It wasn’t his fault the damn Senju was a sight to behold on the battlefield.
Reaching the Senju, Izuna made a beeline for Tobirama, practically buzzing with anticipation over what the Senju brought for him to deal with today. He steadfastly ignored the odd look Madara gave him.
After some fighting, Izuna noticed that Tobirama had yet to bring out any new (or even recently tested) experiments, instead opting for his usual water styles and his well-worn katana.
“What, out of experiments already?” Izuna taunted and felt his heart beat faster when Tobirama smirked back at him.
“Miss being my guinea pig, Uchiha?” He shot back and Izuna would have been insulted, should have , but instead grinned at the banter.
“Oh, please. Don’t tell me you’ve run out of ideas, Senju!”
Tobirama pulled back from their standstill, getting himself enough space to confuse Izuna a bit, and he felt himself tense as Tobirama’s smirk became sharper.
“Oh no. Quite the contrary. In fact, I’m quite interested to see how you’ll deal with this .” Tobirama raised both hands to form an unfamiliar seal, and Izuna could see the fucking chakra pooling in his hands as the sky darkened, setting off alarm bells in his mind.
“Oh no you don’t!” Izuna yelled, lunging forward, his sword poised to strike.
“Too late.” Tobirama replied, his voice strained, and Izuna found himself stopping short, staring agape as nearly a dozen fucking water dragons poured from the sky, flooding the battlefield with water and forcing him and the other Uchiha to dodge and focus on getting themselves to higher ground.
“ Oh, come on! ” He screamed indignantly at Tobirama as Madara yanked him up on a doton-created structure.
His side had called for a hasty retreat, and while he and his clan all looked like drenched and disgruntled cats, Izuna was interested to find that there were no casualties. Part of him wanted to attribute it to Tobirama’s jutsu being an experimental one, but he knew better than any that with that man’s control over water, he could have easily drowned most of them with that surprise move, but hadn’t for some reason.
V.
Izuna was ready.
He’d been able to counter everything that Tobirama had thrown at him for the most part, and he knew he’d finally get the upper hand.
So far the fight was a typical one, with no experiments on Tobirama’s end to throw a wrench into things. Izuna knew that the man likely had something up his sleeve, with the way he continued to avoid his taunts and questions about it, but didn’t know what.
No matter - this time Izuna would get the upper hand, his ego still horribly bruised from that water dragon spectacle only a few months prior. Who did Tobirama think he was, making giant dragon tsunamis out of nothing as if he were some God of Water? It was entirely too flashy, and unfortunately for Izuna and his godforsaken sharingan, he loved flashy.
And being right up close to Tobirama when he unveiled new invention after invention was more than worth the endless bruises and cuts that he inevitably went home with, though he certainly gave as good as he got and always made sure to leave Tobirama with some parting injuries as well. Their bloodbath had become a dance of some sort, and Izuna could see why Madara and Hashirama opted to trade non-lethal blows the way they always did.
Izuna also continued to ignore Madara’s increasingly frequent protests about ‘egging Tobirama on’ and ‘exercising some self-preservation’. He had been able to handle himself just fine against Tobirama for years now, and that wasn’t about to change anytime soon. If anything, Izuna was right on the cusp of pinning Tobirama down at last, he could feel it.
Izuna grinned as he finally found his opening and lunged, his sharingan active. Nothing would get by him, not even Tobirama Senju. At last, he’d take down the White Demon of the Senju Clan. His sword aimed for his side, for a place that would incapacitate, but not kill, not yet.
And then Tobirama fucking vanished.
Izuna couldn’t even process what had happened before a sharp pain bloomed in his side and he dropped his sword, looking down in shock as his side was sliced open.
What the fuck?
Collapsing with a grunt, Izuna held his side as he panted sharply, trying to keep pressure on the wound. Distantly, he heard his brother let out a scream.
Surprisingly, the hands that covered his own were not his brother’s, but Tobirama’s. Looking up, Izuna noted the look of shock and horror on the man’s face, even as the cooling touch of healing chakra seeped into his side. It felt nice.
“You… you didn’t–” Tobirama stammered.
“Not bad. Guess one of your experiments finally worked.” Izuna joked lightly through gritted teeth and Tobirama let out a shaky breath, opening his mouth to respond–
“ Get the hell away from him! ” Madara howled, and the cooling chakra was cut off as his brother grabbed the back of Tobirama’s armor, yanking him back violently before cradling Izuna to his chest.
He missed Tobirama's chakra immediately.
“Izuna, Izuna! Are you–” Madara gasped out, his eyes wet with tears.
Bringing a hand up to cup his brother’s face, Izuna managed a smile. “I’m fine, nii-san. I’m in a whole lot of pain, but I’m fine. Look.”
Madara looked down and finally noticed the half-healed wound that Tobirama had been working on just moments ago. Blinking in confusion, he looked up at Tobirama, who was now half-concealed by Hashirama, who was standing protectively in front of him, though the elder’s expression remained passive.
“Madara…” Hashirama started, but Madara ignored him, calling for a retreat instead.
As he lay in bed, now fully healed and no longer in pain, Izuna couldn’t help but long for Tobirama’s gentle touch again.
Groaning, he dragged his hands over his face. Madara could not know about his new obsession - he didn’t know if he could handle
another
lecture about self-preservation so soon after almost getting stabbed to death.
+1
The whole ceasefire-turned-village-turned-peace thing happened relatively quickly, at least to Izuna. Granted, he wasn’t the one attending the hundreds of meetings that Madara and Hashirama had to, so he mostly just observed as an outsider. He certainly didn’t mind - apparently Hashirama was awful when dealing with technical details, and it was only by the grace of Tobirama and Hashirama’s wife Mito that anything substantial got done.
Madara still didn’t trust or even like Tobirama very much, but at the very least they seemed to be cordial enough with one another in regards to work, and before Izuna realized winter had turned to spring and the first buildings of their new village had been fully completed.
As their clans slowly began moving into the new village, Izuna couldn’t help but feel somewhat disappointed. Not because of the newfound peace, no. He was glad that the endless generations of trauma and war had ended. What disappointed him was the fact that he’d likely no longer see any of Tobirama’s new experiments. Would he even continue them now that there was no war to prepare for? Would he turn his inventor’s skills to the more mundane? From what Madara had told him Tobirama seemed to have taken an interest in the children of the village and wondered if Tobirama would instead become a teacher. In the past, the idea of the White Demon teaching small kids would have made Izuna laugh in disbelief, but now it didn’t seem so far-fetched. For a long while now, he hadn’t thought of Tobirama as a demon, just a rival and equal.
Months passed, and Izuna couldn’t help but feel more and more stir-crazy with each passing day. Peace was nice, but what the hell was he supposed to do? He could only spar with Madara so many times, and with peace between the two clans, Izuna couldn’t even hold any strategy meetings. It was all so… boring.
To make things worse, his thoughts more frequently turned to Tobirama, especially now that he got to see him more often, and outside of combat situations to boot. He kind of hated how keeping tabs on the younger Senju brother became a new pastime for him, even if his mind eagerly filed away any and all details he could find out about him.
The way he favored blue fabrics that looked entirely too soft.
The way he seemed to prefer fresh fish, catching it himself by the river.
The way his white hair would frame his sharp features.
None of the information was important, and yet it really, really was.
It wasn’t until he overheard Hashirama complaining about Tobirama’s endless hours in his lab that he perked up.
“Wait.” He interrupted, barging into the Hokage’s office where Hashirama and Madara were talking.
“Izuna!” Madara chided, but Izuna kept talking.
“Your brother has a lab? He’s still doing those experiments?” He asked and Hashirama looked at him in confusion while Madara took on a long-suffering expression.
“I– yes? Why are you asking?” Hashirama asked slowly and Madara groaned.
“Izuna, don’t–”
“Thanks for letting me know, bye!” And he was gone before Madara could launch into another lecture about how Tobirama Senju couldn’t be trusted.
At this point it was for appearance’s sake - Izuna knew that Madara had long decided that Tobirama was no longer a threat to him or his clan.
Reaching Tobirama’s door, Izuna knocked on it hastily, yet when Tobirama answered, he felt all his questions and demands about his experiments die in his throat.
Tobirama was not in his armor, or in his daily wear. Instead, he was in what looked like a very soft (very loose, his brain unhelpfully supplied) yukata, his hair ruffled and eyes soft.
“Izuna? What brings you here?” He asked and Izuna just stared.
Shifting a little uncomfortably, Tobirama began to speak again, clearly misunderstanding the reason for Izuna’s silence.
“If this is about… our last encounter, I do truly apologize… I didn’t mean… I thought you would counter it like you always do. I meant to seek you out, but between the village and your brother, I–”
“You look so hot right now.” Izuna finally managed, startling Tobirama into silence.
The two stared at each other in bewilderment for a moment before Izuna decided, fuck it , and grabbed Tobirama by the shoulders and yanked him down into a kiss.
Pulling away breathlessly, Tobirama stared at him with wide eyes. “Wh– what–”
“You’ve got a lab, right? For your experiments?” Izuna asked softly and Tobirama blinked at him.
“I… yes.”
Izuna smirked, enjoying the small shiver Tobirama gave in return. “Well. I’ve got some experiments of my own I’d like to try out, if you’re amenable, Senju.”
Slowly, ever so slowly, a small smile appeared on Tobirama’s face, making Izuna’s heart leap. “Well, of course. It’s only fair, after all you’ve been putting up with my experiments for quite some time now.”
Laughing, Izuna shoved Tobirama back into his home, following suit and shutting the door behind them.
Perhaps his experiments wouldn’t be quite so destructive, but he’d certainly make sure to leave some marks that Tobirama would remember for a long, long time.