Madara is still not entirely certain how this happened.
Logically, he knows that he actually is: he remembers the progression of events as well as anyone (well, except that one night with the sake and the shochu and the umeshu, but that's probably unimportant in the grand scheme of things). He knows the hows and the whys and all the arguments in between, but…
But he still doesn't understand how this happened.
As if solely to spite him (and honestly, Madara wouldn't put it past the tetchy bastard), his current bed partner gives a soft, nearly sweet sigh and curls closer, head pillowed on Madara's shoulder. Shaggy white hair, for once not held back by a happuri faceguard, falls over sharp-fine features and tickles Madara's skin, and almost in spite of himself, Madara reaches up with the arm that isn't curled around pale shoulders ropy with muscle and carefully brushes it away. Long-lashed eyes flutter slightly, but don't open, and Madara decides to push his luck. He traces one kunai-callused finger across the thin red lines tattooed on Tobirama's cheeks, then up to the arch of one white brow and over the delicate curve of an ear.
This is hardly the first time he's thought it, but Tobirama is nothing like his older brother, in looks or personality. Beyond their willpower, the two brothers have nothing in common. Now, like this, the differences are even clearer. Hashirama is tall and broad-shouldered and painted in bold lines, always in motion even when asleep. He snores or drools or rolls around, makes a fool of himself and never cares.
Tobirama is silent, always. He's smaller than his brother, leaner, built for speed rather than power—a pale killing moon to Hashirama's ascending sun. Madara has seen him fight, and though he'll likely never say as much, it awes him. Tobirama is his height and a good twenty pounds lighter, but between his ninjutsu, his speed, and his seals he's the equal of anyone.
Madara's equal, which he never thought would happen.
(There are two names on his skin, Hashirama and Tobirama, one written in neat black letters on each wrist. One is a soulmate; the other is his enemy.
Madara supposes he should care which Tobirama is.
He's found that he can't even begin to consider it. The separate steps along divergent paths don't change the fact that the destination remains the same.)