The Yamanaka Clan belongs to Konohagakure no Sato and hails from Hi no Kuni. They are mostly known for their hijutsu, known as Mind Switch or Mind Control, which allows them to access the mind of others and even take over their opponent's body/mind.
The Yamanaka are firm believers in the Will of Fire, as well as the Senju and Uchiha's wish to make of Konoha a place for all to live in. But they also believe in their old rules and traditions, of which a few have remained ingrained in their minds.
The Yamanaka clan is a clan that thinks. The Nara plan, the Akimichi nuture, the Yamanaka gather their thoughts And is is something none of them dare to forget, for it is their minds that are their great prize. The mind is an important tool for the Yamanaka. Not only because they are apt to discern deceit and lies, but also because without a strong mind, they cannot use their secrets upon their prisoners.
The Yamanaka are probably the most ruthless of the Ino-Shika-Cho clans, for they have no grand schemes to save the world, nor food to bribe with. Instead, they are thieves of information, of characters, of people. They delve in the minds of others and take what they need, in some cases even ripping it to shreds with or without care. This, is something important for the younger generations to remember. Mind walking is amazing. But it comes with the price of corruption, greed and violation. Entering one's head means you enter their most sacred and most intimate parts of their soul. And you, as Yamanaka, are not supposed to care about it: you leave it wole if the mission asked for it. If not, you rip it to shreds. After all, a mad man is a silent one, who cannot betray what it has seen and felt in future date...
But most important of all: the Yamanaka shall never leave the Senju, Akimichi or the Nara behind. Without them, the core of the clan's foundations would collapse. For as much a mind is strong, it needs emotions and a nutured body to function.
The Yamanaka have always been in Hi no Kuni, but not always been shinobi. First and foremost, they were gardeners, specialized in exotic flowers as well as meditation methods, owners of a heavy secret.
The clan has small origins of no importance, until a century before Konohagakure no Sato was founded; the first one to own the 'secret' of the Yamanaka, was a young man, who one day when making silly gestures as a child, ended up transferring himself in the body of his sister. Of course, the whole event caused a lot of commotion, but eventually it was left alone, as the boy never managed to reproduce the phenomenon. A generation later, the event reproduced itself, but this time between a Senju and a Yamanaka child. This of course caused even more troubles, as the two clans weren't allies of any sort yet. It was only because of the goodwill of the Senju leader that it did not end up becoming an clan war.
The Senju helped the Yamanaka to harness their secret and to grow it. Children were trained to become shinobi and the adults were conditioned to help this growth. The Yamanaka, for this kindness, swore themselves to always side with the larger clan, and help them reach their dreams. So when Konohagakure no Sato was found, the Yamanaka immediately answered to their call, along with their friends the Akimichi and Nara clans.
In the first years of Konohagakure, the Yamanaka struggled to find their right place among the shinobi ranks. When they were only oblidged to the Senju, they had always been able to help them, for the larger clan would help them adapt. But finding themselves mingled with Uchiha, Sarutobi and so many more, the struggle became more apparent. The Yamanaka skills in those times was still very rudimentary, needing full concentration to be used. There was no time in battle for it, nor was scouting possible, for the hold on the minds was brittle at best.
It were their old friends, the Nara, that allowed them to find a way to harness their strength into true jutsu. Research was being put together, the Akimichi helping them along with along to treat cases of chakra and physical exhaustion by taking the Yamanaka in until recovery. It was quickly discovered that the 'Mind Walk' abilities of the blond shinobi would be the most effective in actual interrogation situations. Of course, they would still be useful in battles, distracting and disrupting the opponents and their teamwork, but the major downside was that the most basic jutsu left the user vulnerable. This discovery started the famous Ino-Shika-Cho teams, that would shine throughout Konoha history with their strength and effectiveness as well as prime example of teamwork.
Once having discovered their qualities as torture and interrogation masters, the Yamanaka decided to focus on this. While they forced their way through prisoners and dead bodies from the enemies fallen in the First Shinobi War, they also developed jutsu that would allow mental recovery of those who were deemed lost. One of their great victories in this, was bringing back an Uchiha that had fallen in a coma for four months. Their other notable victory was the breaking of several jounin minds and extracting information that saved many lives.
It was in the times of this First Shinobi War and following the Second Shinobi War, that the Yamanaka started to grow ambitious. They no longer had the wish to remain behind and solely focus upon interrogation.
Truth be told, they wanted power, but also a stronger position in the village. The Uchiha and Senju would always be their leaders, but they refused to have to bow down to Hyuuga or Inuzuka. When the first Hokage died, they felt themselves angry at the idea of not having another Senju as their leader - the loss of the Hokage had hit them harder than they had anticipated. A jealous sentiment reigned among their ranks; why should an Inuzuka be Hokage if they had been for longer alongside the Senju? Why wasn't it an Uchiha at least? But then it was clear: they were weak. None of them were superb fighters, most of them remaining behind the walls of Konoha, rarely stepping truly in battle. And that wouldn't do for them any longer.
The Yamanaka from those times on, grew ruthless, cold and fierce, the Will of Fire burning through them. Many changed their battle methods. No longer relying almost solely on their clan techniques, adding vicious genjutsu to complete the Ino-Shika-Cho teams completely. Their goal was to destroy the minds of their enemies, leaving only enough to bring the last pieces of information in interrogation.
They were aiming to be feared, by the mere mention of their name and their ambition would be brought on over the generations to come...
The Yamanaka clan has a fairly simple hierarchy.
A leader has been groomed to reign over the clan since it's birth. A specific line in the clan has been chosen to bare the heirs and thus will be asked to bring in regularly new, strong blood in their midst. A heir or heiress shall be designated once they have reached the rank of chuunin, when their chances of survival in the cruel shinobi world have truly been strengthened. They are not chosen upon age, but upon skill, wisdom and humbleness. It wouldn't do to have an arrogant toe-rag to be at their head and destroy all they had worked for through the ages.
A council of five is right below the leader. They give advice and if they decide the leader is incapable of protecting the clan's interests, they can bring him down after having gotten at least 60% vote from the whole clan.
The Inquisition is a group of highly specialized Yamanaka, trained with the greatest clan jutsu, as well as the sharpest possible training in fuuinjutsu and genjutsu respectively. They protect the compounds, but are usually also part of the Torture and Interrogation squad that Konoha possesses. This group of shinobi are of all ranks, even genin, as long they have great potential and strength in the art of physchological warfare. It is tradition that the Clan Leader was part of it and that it's heir(ess) also takes a role in this squad. The highest secrets of interrogation that the Yamanaka might have is held by the Inquisition and it is only through them that one can learn it.
The members are simple shinobi or civilans.
The Yamanaka have created a large variety of hijutsu that all concern the human and animal mind. In all and all, they can control the mind, erase memories, create false memories, extract information, force information into the mind, destroy and some form of telepathy as well. They have also a variety of more medical versions of their jutsu. Bringing people back from a coma is possible now on some occasions, as well as forcing them into one.
But those techniques are also limited and with various weaknesses. Most of the jutsu force the consciousness of the user out of the body, leaving it vulnerable without a friend or ally nearby. The user can also be repelled by stronger minds, the most dangerous ones being the Jinchuuriki's. Lasty, they can also get 'lost' in the most violent and chaotic consciousness of those they attack, bringing them to or locked up forever, or simply die while in the mind of their opponent.
Most techniques are secret - no one outside of the clan shall ever be taught, not even to those adopted inside of it. Only those with the Yamanaka blood and that keep up the name would be taught.
Some Yamanaka are born with a sensory ability. This is rather rare, but when it does happen, it is a great boon. Similar to some Uzumaki, they can sense chakra signatures and certain strong emotions around them, although in a far smaller radius. It is the least well known ability of the clan, and because of the rarity, the amount of scouting jutsu the Yamanaka have made is very limited.
It is rumored that the Yamanaka have more than simple hijutsu. This of course, is false, although not a completely wrong assumption. The Yamanaka are strong willed and strong of mind as well. They have very structured thoughts and manners, training their minds to resist any sort of control attempted upon them. This training and inheritance also made them the only ones capable of using their Hijutsu - different hand seals to mold their chakra with and needing a particular mind set to be able to 'mind walk' made it impossible of outsiders to use the jutsu. Uchiha of course, could copy them, but the results could easily lead to madness, comas or simply nothing, for the hand seals did not respond to their orders.
Interrogation & Torture
Although this is not exactly a genetic trait, the Yamanaka have a special preference for this part of the shinobi life. Training regimens, scaring tactics, torture methods are part of those who aim for ANBU and the T&I and the Yamanaka specialize in teaching these to new recruits. Their creativity in this is renown and feared.
From young age on, Yamanaka children are taught to have a good control over their emotions and mind as well as how to impress those around them. In no means the clan teaches them to abandon emotions, but to hold and use them to their advantage. Facial expressions are broken down, analyzed and reintroduced, along with various quirks and subconscious actions. It is not unusual for the Yamanaka to have one or two of those on purpose, so to give the wrong impression upon their enemies, as well as to calm down their own allies.