Senju Hashirama watched as the wooden spear punched a hole through Uchiha Madara's chest. The man coughed up blood and fell to the ground. With it's summoner dead, the Kyuubi vanished in a massive flash of fire. Hashirama guessed that the creature was glad the battle was over. Throughout the whole fight the two ninja had been struggling to gain control of the fox, Madara with his Mangekyo Sharingan and Hashirama with his Mokuton techniques. The fox was probably reveling in it's freedom.
Hashirama turned to leave when he thought he felt a sliver of chakra coming from Madara. His first thought was to dismiss the possibility of the Uchiha still being alive. A summoned creature only leaves if the summoner has died, and the wooden spear had to have pierced at least two vital spots. His instinct was to leave Madara for dead and return to the village. He had suffered a great many wounds during the fight and he needed medical attention.
But there was a tiny voice in the back of his head that was screaming at him to go check on Madara.
While he didn't know it, the decision he was on the verge of making was one of the most important ones ever. His choice would influence countless numbers of lives.
All the evidence was pointing at the fact that the fight was over, and he needed to leave. But he decided to go ahead and make sure that the traitor had died. He turned and walked across the river to the armored corpse. For some reason he wasn't surprised when the man drew a shaky breath and tried to push himself up off the ground. Hashirama grabbed the spear that stuck out of his back and gave it a hard yank, pulling Madara over backward so he landed on his back, looking up at his enemy. He didn't even have enough chakra to use a normal Sharingan, let alone his Mangekyo Sharingan. Despite his weakness, Madara managed to spit blood at Hashirama's feet.
"Go to hell." The Uchiha snapped at him. "That's where you damn Senju belong."
"I could say the same thing about your Uchiha relatives," Hashirama replied angrily.
"Don't you dare insult my clan! We're elite warriors, we're nothing like you Senju bastards!"
"You have done just as much evil as we have over the centuries. Neither clan is free of taint or guilt or blame, the sooner we all realize that the better. But we made an alliance, and you chose to break it and fight me to the death, yet again. Unlike all those times we fought on the battlefield, you don't have anyone to come save you this time. So now, you will die."
"Only because my clan has become a bunch of idiots who think they can trust you," Madara spat at him again. "They'll regret it sooner or later, I just know it."
"You're wrong. My clan will never break our alliance. And I trust your clan not to break it either."
"Well you better hope they stay stupid then or they'll try to get rid of you before you can get rid of them." Hashirama sighed. There was no point in continuing their argument. He pulled out a kunai and reached down. Just before he cut Madara's throat, the man spoke again. "Wait." Something in his voice made Hashirama hesitate.
"Why? I won't spare you no matter what you say."
"I know that, I don't want you to take pity on me. I did a lot of things for the sake of my clan, and I want to ask you for a favor." Hashirama was intrigued.
"Don't let my clan crumble and fall. Make sure we continue living. And make sure we are feared and respected."
"I will do as much as I can to ensure all of that," Hashirama tried to assure his enemy.
"I'd say thank you, but you're a Senju and I'm an Uchiha," Madara told him. Hashirama actually chuckled at that.
"I won't tell anyone that you thanked your lifelong enemy for granting a dead man's last favor." Madara mulled it over for a moment.
"Oh, just go ahead and cut my throat. You're not gonna get a thank you." Hashirama shrugged, then reached down and neatly cut Madara's throat open. His blood poured onto the ground. To his credit, Madara didn't even grimace in pain as he died.
Senju Hashirama, the First Hokage of Konohagakure, picked up the corpse and left the Valley of the End. Without ever knowing it, he had just saved hundreds, if not thousands of lives, all thanks to one small decision.
One decision that changed everything.