[ 1 ]
His sword goes through Izuna, deceptively easy, and for a second Tobirama cannot believe that he hadn't missed.
He feels the roar before it issues from Madara's throat, because that tightly controlled chakra bursts into a million jagged fragments, each angrily seeking to maim kill destroy.
But Izuna inhales, a broken sound, and that lethal focus shifts from him to the younger Uchiha.
This is the moment Tobirama realises that, for the Uchiha, a single emotion incinerates all others. He discards the misconception that they are born with hatred in their hearts, but now he sees them as more dangerous than ever.
If Uchiha Madara loved his brother any less, he would be a dead man.
[ 2 ]
The world is charred at the edges, space slightly distorted, when Madara sees it through the eyes of the clones. Something that looks to be within reach could be metres away, but there is no mistaking this.
Where before there had been only stone and potential there is a face. (He had once envisaged his face there before dismissing the idea as folly. He has no desire to lead Konoha, and gods, not statues, are truly immortal.) Even in stone, Senju Tobirama looks constipated, as if everyone in the world owes him a debt. What a small, bitter man.
Madara does owe him a debt, though. He owes him a sword in his gut, the chance to stare incredulously at him as he takes his final breath, the opportunity to atone for his sins.
Izuna's eyes throb, hot and sudden, like a fervent promise.
[ 3 ]
Uchiha Madara never just enters a room. He fills it with whatever mood he's in, and usually this creates a subtle hum of menace. Today the air is still, eerily so. Tobirama tries not to think about what exactly had thawed the man's temperament even as Sharingan-red eyes scan the scrolls sprawled around the room.
He hadn't taken pains to hide his work, since he'd not even thought of the possibility that Madara would take any sort of interest. The Uchiha rarely takes an interest in anything, and Tobirama wonders if he is lost.
He is. Lost in thought.
It takes all of his self-control to ignore the other man and continue working on the equation.
"You're stuck."
Tobirama doesn't answer, because there is no point in confirming the truth. Developing the other parts of the technique had been almost frighteningly simple. He'd begun by studying the Yamanaka techniques. They called it "mind-transfer", but Tobirama saw their techniques as imposing a foreign will — or "soul" — upon another body. He then tried to apply the same principle to unhoused souls, working with Uzumaki Mito to create seals that could draw and capture the intangible. But progress stalled after that, as recalled souls evaporated like water on a hot day. They were inevitably pulled back to the underworld, no matter how he adjusted the seals or fortified the walls of empty vessels.
Madara's fingers float over one of the corpses, face angled as if speaking to it. Shadows gather in the contours of his expression. "You can't cheat death. You have to bargain with him."
Tobirama swallows, the words swirling in his head and forming inky images of sacrificial rituals. What was it that people said about dealing with the devil?
Oh, yeah.
Don't.
"A life for a life. Nothing fairer than that."
Something behind those red eyes flashes for a split-second. Tobirama almost ducks, expecting a sword to fly at his neck, though neither of them are armed. A life for a life. The blow doesn't come, and steel isn't drawn, but the desire still flares, right in the molten core of Madara's black-hot chakra. Tobirama for Izuna.
Madara knows he cannot hide it from Tobirama. He doesn't even try.
[ 4 ]
During the third week of their acquaintance, Madara follows Hashirama.
The other boy is cautious enough, snaking through obscure routes, doubling back and leaving false trails, but Uchiha children learn to not be seen even earlier than they learn to speak.
What he sees confirms his suspicions about Hashirama's origins:
Arm looped around shoulders, the Senju clan symbol worn against light hair, laughter and small smiles, a closeness that he's never experienced, not even with Izuna.
Who is that boy, he seethes, even though it is so irrational. He has known Hashirama for less than a month. But still he imagines burning the smaller child — Tobirama, his companion had said with such affection in his voice — to a blackened crisp, and not because he is a Senju.
He had thought Hashirama to be like him, different, friendless. Madara hates being wrong.
[ 0 ]
His lips are numb.
I'm going to die.
Tobirama understands, now, his mother's supernatural calm during the last days of her life. When one can be certain of death, it ceases to be a terrifying unknown.
He does not, cannot, hate his brother for being the one to execute his death. Peace is bigger than him. It's bigger than the both of them.
But he glares at the man on the ground and wonders how, even in his current position of vulnerability, Madara manages to be so unnecessarily cruel and petty—
—then Hashirama turns the blade on himself and Sharingan eyes spin in panic and when Tobirama finally breathes it is in comprehension because it had never been about him.
If Uchiha Madara loved his brother any less, he would be a dead man.
Notes
Written as a gift for the prompt: "Tobirama having trouble solving a crucial equation in Edo Tensei and Madara solves it for him."