Hashirama called Madara is gift from the divine, and in his more whimsical moments Tobirama had to admit he may be right. They seemed almost like two parts of a whole, his brother and the Uchiha heir. Both bore too much responsibility on their young shoulders, both had one brother left to protect, and both (according to Hashirama) dreamed of peace. They were also both prodigies on the battle field. Forced to fight one another, soon the only ones physically able to counter the other. They grew apart, and yet together. Soulmates was perhaps a fitting word for what they seemed to be.
Were Tobirama in an even more philosophical mood he might even say the same of himself and Izuna. Younger brothers both just as determined to protect their elders as their brothers were to protect them. Rivals that clashed again and again with no clear victor. A sword always blocking the other’s path. They seemed as drawn to each other as their elder brothers were. Two sets of boys from feuding clans lost in a never-ending fight against each other.
Tobirama had never had the chance to befriend Izuna, never truly had the chance to get to know him. He mourned that sometimes. From the speed his rival was able to learn, understand, predict, and counter his new jutsus Tobirama could tell he was intelligent. He wondered sometimes, how much more he could accomplish if Izuna was beside to help him pick out weaknesses in his jutsu, not to best him with but to help him improve them. Wondered how much faster the Sharingan would help him be in his experiments.
Such thoughts were useless in the long run, but still he couldn’t help but wonder. Every time they clashed. Every time his brother’s eyes sought out Madara on the battle field and his sought out Izuna. Each time their swords clanged together, he wondered.
He didn’t wish, for he knew nothing would come of it, but he did wonder. Izuna had ever been his perfect foil. Like Madara and Hashirama they had practically grown up together. He remembered Izuna’s growth as well as he remembered his own. His rival was as constant a prescience in his life as his brother was. So yes, perhaps soulmates was a fitting term. Boys raised to match each other. Boys raised to fight, again, and again, and again. Boys raised to war who knew the other as well as they knew themselves. Boys told that their worth would only be proven when the other lay dead. Drawn invariably together through the endless fighting. A far less romantic idea than the civilians had of soulmates, but fitting for the shinobi they had always been.