Jounin led teams, those slated to actually pass, are designed with specific functions in mind. For example, the Aburame, Hyuuga, and Inuzuka team are for tracking, the Ino-Shika-Chou for, essentially, guerrilla fighting against samurai and bandits. Team Seven has always been for heavy hitters, while Team Nine are for escort missions. That is not to say that some teams cannot fulfill other roles. Ino-Shika-Chou make excellent bodyguards as well, and Team Seven has always been more than just brute strength. Not that their specialties matter for much during lowly D-rank missions, anyway.
Team One is rare, hardly ever created, because Team One is designated for medics. It had been considered, a few years ago, when Yakushi-sensei’s adopted son was on the edge of graduation. But none of his classmates matched his potential for healing, and so a Team Six, general support, was created instead.
A person would think that, with a genjutsu specialist, a medic, and a fuinjutsu user, their team would be made into a a Team Six as well. But the genjutsu specialist has a fondness for traps, the medic has a talent in taijutsu, and the fuinjutsu user has a chakra reserve four times the size a ninja twice her age.
Teams are designed with a specific purpose in mind, whether they fulfill that purpose or not depends on how well they can learn. Team Five, simply known as the retrieval team, requires a little more adaptability than most teams.
Team Four is a throw away designation, a filler team for graduates that aren’t primed to be trained by the elite. There has never been a Team Four that passed. Which, makes sense, considering the bad luck surrounding number four. Superstition might be silly, but no need to tempt fate any further. As it is, the reputation of Team Four being a career killer is enough to ward away any inquiries.
But perhaps it would be better to say that Team Four isn’t a filler so much as it is temporary. There are records, hidden away in the darkest corners of high clearance files, that show activity under Team Four’s name. A mission here and there, never with the same team, much of it still redacted. To those in the know, Team Four is the assassination team. Team Four is an audition for ANBU.
A/N: Uh… so technically Counterpoise is the title for my attempt at a Naruto’s twin!SIOC fic. I don’t really want to pursue it? Or at least, not as it is. I may adapt it into a different fandom or different story. Um.. if you’re curious, though, you can look at my brainstorming lj posts here.
And, also, I was trying to figure out how team numbers work and why Team Sevens always seem to be the huge legendary guys. So, probably, Team Seven is specifically slated for heavy hitters (or, potential heavy hitters).
edit: Tweaking my headcanon for team designations (though not very much, all things considered) given the fact that baby!Itachi was put on Team Two with a boy who basically called himself Tenma Lord of Speed and a girl who, given the awful awful sexism in this series, unsurprisingly got shunted into retiring to become a waitress even though she studied medicine in the Academy?! And while she doesn’t quite match up with the new designation either, it’s better than my original that Team Two was genjutsu. Perhaps she also happened to be the fastest kunoichi and having a healer on any team certainly isn’t a downside.
Team One – Medic
Team Two – Stealth/Speed (Vanguard)
Team Three – Genjutsu/Barrier (Defense?)
Team Four – (code for ANBU trainees/assassination)
Team Five – “Retrieval”
Team Six – General Support
Team Seven – Heavy Hitter
Team Eight – Tracking/Hunting
Team Nine – Bodyguard/Escort/Courier
Team Ten – Infiltration/Siege
So basically, the Academy does actually create genin teams that the students would be well suited for if the assigned jounin sensei commits to it/sees potential/etc. Like with the idea that Dreaming of Sunshine’s Team One would have passed if they had a combat medic for a jounin-sensei (leading to mine and @kuipernebula‘s Team Medic AU. The Academy teachers probably don’t have much say in the jounin assignments, but they can do their best to bundle the genin into appealing bunches (if… that makes any sense) and hope the Hokage wrangles the jounin into place (more often than not, that’s a no)