Learning that his soulmate was a Senju had been difficult but it had been nothing Madara couldn't deal with. It could help him with peace, he had rationalized, help him save his three younger brothers, even if his elder brother had been taken from him. Tajima might have denied him his ceasefire, but Madara would be clan head after and it's not like he's ever given up on his dream. A dream borne between two children forced to grow up too fast in a bloody war they had no hand in.
Learning that his soulmate, the one to match him more fully and perfectly than any other, was Senju Tobirama, a demon for all he was only Izuna's age? Learning this while on the battlefield? While his father, while not the best but still his family, was cut down in front of him? It soured those ideas.
When Hashirama's letter arrived, the words speaking of peace and, more immediately, a ceasefire... Madara almost turned it down. Almost rejected it in the manner his father had. But something in him longs for Tobirama. Longs to know Tobirama beyond the cold mask displayed on the battlefield. Tobirama, after all, had done for the peace what Madara and Hashirama could not bring themselves to do. Tobirama bought the lives of the Senju and Uchiha shinobi and civilians with the blood of Madara's father and who is he to let that go to waste? To allow his beloved father to die in vain like so many before?
The Elders are difficult to deal with and convince. Togakushi stands with him, though, as does Hikaku. Kuro and Izuna are far more wary but, to Madara's relief, they don't undermine his authority (so new, so fresh and weak in the wake of Tajima's death), content to trust him.
The majority of the clan accepts the peace, accepts Madara's decision, but the hesitance to put any trust in Tobirama is expected.
The Uchiha Elders and Heirs end up on the opposite side of the Naka as a matching contingency from the Senju. Madara leading his clan, Hashirama and Tobirama leading theirs. Kuro stands beside him on his left, Togakushi and Izuna a solid presence at his right.
Kawarama and Itama are on either sides of the Elders, looking more like guards (prison guards, he thinks, and he asks himself just what his soulmate has been prepared to do) than the heirs they are.
When Madara shakes Hashirama's hand, he can see the relief, excitement, and happiness warring in his eyes. When he takes Tobirama, he feels like the world has been torn out from under him. Tobirama's hand tightens almost imperceptibly around his, grounding him at their soul bond settles. The colour that floods back into the Senju is almost overwhelming but Tobirama hardly changes, beyond the vibrant, soulful red that bleeds into his eyes.
The albino, so out of place amongst his clan (and suddenly the nickname White Demon makes so much more sense to him, with his white hair and pale skin), offers a small, sharp smile that holds promises and an edge of vicious, smug victory.
Madara drops his soulmate's hand, stepping back as he ignores the silence that came over the muttering, unhappy Elders. This peace Madara has believed was his and Hashirama's, something they had worked for and fought for and bled for, but it's not. It is, as he's come to realize, Tobirama's.
And Tobirama alone deserves to lead them into it.