Every Hokage after Hashirama has been a member of a team seven. Tobirama led the first team seven that had ever been assigned the number, and after that, students of his student took up the position.
In a way, it became tradition. However, team seven was not just a team from which the Hokage was chosen, it was also a team that people learned the hard way to watch over protectively. It was, after all, a team where great or terrible things happened. Sometimes, it was both.
The first team was lucky, and all their members lived to an old age while attaining prominent positions in the village. Hiruzen Sarutobi was the longest lived Hokage, while Homura Mitokado and Koharu Utatane became council members and trusted advisors in the village.
The next team seven was not so lucky. Tsunade was driven deep into unhappiness for much of her life, Jiraiya fled the responsibilities left to him by his student even as he gained notoriety for his stories, and Orochimaru. Well, what can be said about Orochimaru but that he made a great many mistakes and eventually paid for them?
Not every team was as famous as these however. For a brief time, Sakumo Hatake had a genin team, but it was an unfortunate time to have students, and they didn't make it out of the rank during the second war. Later, everyone old enough knew of his failure in attempting to make up those mistakes. They knew he wouldn't leave teammates behind, and it ruined his life. He was blamed for a war, and for him, there was simply no winning.
In an effort to wipe away the sharp and sudden failure of that team, the number was quickly traded to another, and this one was led by Jiraiya, continuing the line of the first team with somewhat better results. Minato Namikaze became a Hokage. The other two... well, they faded into obscurity, though records say that at least their lives went on after they graduated out of the number into being chunin and the team broke apart.
Minato was the next to take the number, this time for sentimentality as his team came in parts, and not all of them were genin together in the first place. That might have been his mistake, as his team was faced with tragedy when they stayed together after going up the ranks. Obito Uchiha was crushed to 'death', and Kakashi Hatake, already having been hit with the team seven jinx by way of his father's suicide, was hit again with the grief of this new death. There was of course what happened to Rin, and Minato... The history books go on long and loud about Minato, who died a glorious, much too young death.
Somehow, it never occurred to anyone to stop giving out the number after that. Most especially it didn't occur to anyone to stop giving it to the prodigies of the village, as the next was handed to a team of four of which three made names for themselves. The one who died was killed not even six months into being a genin because he was much too determined to prove that he was ever so much better than the seven year old on the team. The seven year old, Itachi Uchiha, wanted nothing more than for everyone in his team to get home safely so this was quite the blow. Thankfully, Iruka Umino was there to reel the younger child in, or there might have been two deaths that day before their sensei, Ibiki Morino, arrived to help them. Everyone knows what happened to Itachi, just as everyone simply knows Iruka, and the less said about Ibiki the better, most would agree.
Someone might finally have gotten a clue, then, because for a while, team seven was, while used, was also not filled with those who had the potential to utterly rewrite the history books with their achievements. The next two teams went down in obscurity, and while not all members survived, their deaths were also not the sorts which created the great tragedies.
It was not to last, and that was, while expected, still incredibly unfortunate. The current team had the most potential and the most history. This team had a sensei who was both son and student of team seven, Kakashi. It had the brother of one of the lesser known sevens, Sasuke Uchiha. It had another son of seven, but this time compounded by the other ties he didn't even know he had, Naruto Uzumaki. And last, last there was the girl who was eternally trying to catch up with her team, because the rest of them had a history and legacy to live up to, and her name was Sakura Haruno.
What happened to them could be called no less tragic than any other seven, but this time, who was watching? Who remembered to watch?
And that was the mistake.
Note: History has a way of repeating itself, no matter how hard people try to stop it from doing so. Sometimes, it's because they miss that vital detail that says 'I've been to this place before', and other times, it's because they weren't looking at the obvious link between A and B. Or, in this case, between Seven to Seven.
