The Tantesu clan reside in Iwagakure no Sato and originated from the very same lands. The clan is renowned for their kekkei tota called Koton, or Steel Release. They currently are held in high regard within the Iwagakure community.
Above all, the Tantetsu value their family and friends over any sort of established organization such as a village. They therefore tend to be a very close-ranked and introverted clan, with many of the members spending most days of the week underground with the Grand Forges and if not, then in their familial forges creating art, weapons, armor, etc.
They are not an overly ambitious clan, however they do tend to maintain a semi-wealthy standard of living simply because they once ruled their own country, though they do not discount the need for hard work. In fact clan members that are naturally lazy are often shunned, leading them to be incredibly efficient workers but at the same time leading to problems such as anxiety and stress.
When a clan member comes of age, usually at age 18, they are tasked with forging their own set of armor from any material. This armor is usually chakra reactive and almost always unique to the person wearing it, designed to perfectly suit their fighting style.
The history of the Tantetsu Clan is littered with the bodies of their former comrades, a testament to the determination of the clan to survive at any cost and eliminate all those who hurt one of their own. As such, the Tantetsu keep their history a close-guarded secret, with very few people outside the clan aware of their actions before joining Iwagakure. As far as anyone else is concerned, they appear in the history books as if they had always been there. Ambitious, powerful and intent on preserving sacred tradition.
The story of the Tantetsu begins in the lowly country of Uma no Kuni, located in what is now northern Tsuchi no Kuni. A very wealthy, powerful state run by the Samurai of old and their Ashigaru retainers. Ruled by the now extinct Hōjō Clan, who were known as master castle-builders, Uma no Kuni thrived on it's tradesmen and imported a great deal of food from the coast and their neighboring country to the west, Yari no Kuni, ruled by the Otomō Clan. Hōjō Hidekatsu, the leader of the Hōjō Clan, and Otomō Matsunaga, leader of the Otomō Clan, were brother-in-laws who loved each other's company and as such the two countries were tied in an alliance of brotherly love and respect.
However, when Otomō Matsunaga died under mysterious circumstances, it was the Hōjō Clan who were quickly blamed for the death of their most auspicious leader and as such the two countries became locked in a brutal war. A war that could not be settled with acquisition of land or profit; both would be satisfied only when the other was totally destroyed. And as such it was a conflict that would not be solved only with swords and assassins, but also with political alliance.
And that's where the Tantetsu Clan come in. Loyal retainers to the Hōjō who had assisted Hidekatsu's father in his total unification of Uma no Kuni, they were as much blood brothers to the Hōjō as the Otomō once were. At the time they were but a clan of samurai, rather than shinobi, wielding the blades they themselves had forged using ancient techniques and materials passed down over the generations. Fierce and ruthless warriors, even their name struck fear into the hearts of Otomō soldiers. And their young leaders, the twins Tantetsu Niibō and Sanbō, were known for being exceptional fighters, wielding their pair of battleaxe's as they tore through countless ashigaru every time they were sent into battle.
The conflict lasted over 40 years, with all three clans shuffling through leaders endlessly. Some were killed in battle, others assassinated, others imprisoned and tortured to the edge of their sanity and sometimes beyond. Eventually they realized that in order to keep fighting despite depleting numbers, they would have to produce more and more heirs. And as such, an agreement between the Hōjō and the Tantetsu was reached, wherein the daughter of Tantetsu Niibō, Tantetsu Kōhime, would marry the heir of the Hōjō Clan, thus binding the two clans together by blood and brotherhood.
Though Kōhime was an ambitious soul, and was dissatisfied with both her new lover and the way his clan had treated hers despite everything they had done for them. And so the first opportunity she got, she not only poisoned her husband, but also her brother who had taken the leadership of the Tantetsu. Having bribed several officials in the courts of Uma no Kuni, Kōhime was now in a position of absolute power over her clan and over the Hōjō, so much so that the leader of the Hōjō died suddenly of shock when he found out that his daughter-in-law had turned his entire clan against him.
And so the two clans merged fully under the name of Tantetsu, quashing all form of rebellion within the clans themselves and slaughtering the Otomō without mercy until they were but a shadow of their former self, fleeing the capital of Yari no Kuni in fright as the Tantetsu Clan marched through the gates. Suddenly the minor retainers of the Hōjō had found themselves the rules of not one, but two large countries.
Eventually Kōhime re-married to the shinobi she had hired to poison her brother, a man under the name of Gegetsu Ushio. And as such, the clan was officially transformed into one of the first true shinobi clans, developing significant control over the elements of Katon, Suiton and Doton.
When the Daimyō of the massive country to the south, Tsuchi no Kuni, started marching northward, instead of fighting Kōhime simply asked to rule over her lands as a retainer to the Tsuchi Daimyō, realizing that she had no hope of winning against such a massive army by herself, even with her shinobi husband. And as such, the Tantetsu lent their powerful smithing abilities to the Tsuchi Daimyō, aiding him in the expansion of his realm into what it is today.
As the world began to evolve into a more shinobi-centric attitude, at first the Tantetsu were skeptical of the hidden village set-up that many other countries had adopted, even with the rather large shinobi presence within the clan itself. The leader at the time, the grandson of Tantetsu Kōhime, Tantetsu Otemori, was given a strict ultimatum by the Tsuchi Daimyō which told him to make a decision on whether or not to join Iwagakure as it was being set up or never have the opportunity to join it again.
Originally the consensus was to remain apart from the shinobi village, sequestered in their halls and ruling over their lands. However, a small section of the clan were determined for the Tantetsu to join in the formation of Iwagakure and went to visit the Daimyō personally, claiming that the current leader of the clan was an illegitimate descendant of Kōhime and should be deposed in favour of his younger brother Tantetsu Kihō. And with the help of the Daimyō, Otemori was assassinated and replaced, with the Tantetsu opting to abandon their keeps in the north and become one with the shinobi age.
Their skill in forging weapons was greatly appreciated in the early days of the village and the once isolated clan learned many tricks from the much more experienced wartime shinobi who had congregated to Iwagakure. The clan grew exponentially, until they numbered much more than many other clans in the village and as such demanded more land be given to them within it's walls to accommodate the growing population. When the other clans refused to give them such space, the Tantetsu at first considered responding with violence, but cooler heads prevailed and instead they requested permission to build beneath the earth of Iwagakure, creating a vast complex of forges while their people lived above ground.
The space was still rather cramped, even with the forges beneath the earth instead of above ground, however the clan soon became accustomed to these tight conditions and thrived, leading to what they called the 'Golden Age'.
Over the course of several decades, the clan expanded and grew, refining their Kōton far beyond anything anyone thought possible. Weapons were created specifically designed for the slaughter of hundreds, if not thousands of people. Wars broke out between Iwagakure and other nations. And the clan simultaneously profited from conflict and suffered as a result of it. Their work was in high demand, kunai and shuriken being created by the dozens every second. War was business. And business was booming.
Their fighting skills were nothing to sneer at either, proving to be powerful warriors both from their Kekkei Tōta and their use of weapons, each member of the Tantetsu worth 20 soldiers on their own. But an important distinction was made. The clan fought to protect themselves, not the village. They valued their family and friends over the village itself and as such did not specifically seek fighting, despite their reputation for being impetuous.
It was then that Tantetsu Jūmaru took over leadership. An older man, starting his dominion over the clan at the age of 47, Jūmaru made it his duty to put into place rituals and rites to prevent Genin from learning the secrets of Kōton until they were truly ready. This increased the average life span of Tantetsu clan members greatly, ensuring that Genin were not used for dangerous missions simply because of their Kekkei Tōta. He also implemented the ritual and festival of leadership, where the leader would be presented with Kōhime or Ushio's ceremonial marching armor, depending on their gender and the festival giving the chance for Tantetsu clan members to show their artistry rather than simply relying on their abilities in combat. These conventions set the foundations of the Tantetsu clan to this very day.
The hierarchy of the Tantetsu Clan is a simple one, relying on central figure of governance, that being the Clan leader. However the Clan Leader isn't necessarily considered to have absolute power. Rather they are kept in check by the elders of the clan as well as a small committee of younger prominent members. As such, the hierarchy of the Tantetsu could be likened more to a republic than a dictatorship.
When a new leader is 'crowned' as it were, they are given the title of 'Kōhime' or 'Gegetsu' depending on their gender, referencing the clan's 'founders'. This acts similar to a title, coming after the Clan Leader's name like an honorific; for example, Tantetsu Nerukō-kōhime.
In general, the Tantetsu Clan are shinobi focused entirely on defense and sheer strength. For that very reason, most fail to meet the basic definition of a shinobi and instead could be considered warriors or guardians of their home and family. Using their infamous Steel Release to great effect against any who would threaten them, the Tantetsu are proud, fierce, determined and overall incredibly powerful, most working in the Grand Forges from very young ages and developing an impressive physicality as a result.
Born from the combination of Katon, Suiton and Doton, Kōton [Steel Release] is the manipulation of the alloy born from iron and carbon. At it's base form, it is the creation of structures or weapons from this substance and the control of said structures through chakra, similar to Doton. Iron and carbon molecules are collected in the earth, then rapidly heated using Katon chakra, squashed together using Doton chakra and then cooled using Suiton chakra, hence the combination. Normally such a quick process would result in very large impurities in the resulting steel, however with the Tantetsu's long history of forging and experience using this process, they have created a very specific balance of chakra and the way the molecules are moved in such a way that impurities only very rarely appear and as such the steel is strong and flexible.
Before Genin of the clan are allowed to learn how to manipulate Kōton, they must first learn how to properly handle the three elements that make it up, especially Doton. As such, many Genin and younger members of the clan work as 'Shifters', pushing ore to the higher levels of the Grand Forges using Doton or as 'Coolers', blasting water into the Grand Forges after their work is completed. The coming of age task clan members go through is known as the 'Rite by Creation' and insists that the clan member create a weapon using their three elements but without utilizing Kōton. The larger or more powerful the weapon, the more renown the clan member won for themselves, the very minimum being a kunai or shuriken. Through such practices they learn the ability to perfectly forge metals, an ability required for the usage of Kōton and as such they earn the rite to be taught techniques in the art of steel.
Most basic Kōton techniques are indeed modeled after Doton techniques, creating thick walls, domes, pillars or other rigid structures that offer defense and control of the battlefield. Offensive Kōton techniques, while indeed powerful, are less common and usually consist of the creation of weapons such as kunai or shuriken for throwing at an enemy. However, in recent years certain clan members have been experimenting with the possibility of utilizing molten steel as a medium for offensive techniques. The issue is that in this state the steel is much more unstable and difficult to control, making it a non-advised usage of Kōton, to the point where several of the clan elders actively condemn the practice. There is no doubt of it's power, however even the most skilled of Kōton-users are advised to utilize extreme caution.
Another unique feature to Kōton that has been added thanks to modern experimentation with the style, is the idea of substituting an amount of carbon in the forging process for other elements, such as tungsten or nickel. Though such practices are very alien to the clan's previous ideology, it does present the created steel with additional benefits, such as increased melting point, lack of magnetic attraction or increased malleability, depending on the alloying material used. However, doing that costs much more chakra and requires a greater degree of chakra control than the average clan member, in addition to the fact that such possibilities are not taught to clan members until very near the end of their tutelage, sometimes into their mid-twenties, giving them much less time to adapt to the idea.
Most, if not all, clan members of the Tantetsu clan are monstrously strong both in terms of their genes and growing up as workers in the Grand Forges. Although in the past this strength was used mainly for hauling and loading ore, advanced forging techniques have required stronger and stronger arms to utilize as the world progresses in terms of technology. As such, it's not unusual for a fully grown adult Tantetsu clan member to breach 7ft tall and have biceps almost as big as their own head. And that's both genders. The issue with being so huge and burly however, is that their speed suffers in equal measure, making them easier to outrun as compared to regular shinobi of their rank.
That being said, what they lack in speed, they make up in stamina and endurance. Where a regular shinobi would tire out, the Tantetsu keep running, oblivious to the pain tearing through their muscles or the kunai in their shoulder, they keep going with a determination that is both admirable and scary. Often a particularly large Tantetsu clan member has shrugged off a barrage of powerful Taijutsu strikes and continued swinging, even without utilizing any Kōton techniques.
Another aspect to their awe-inspiring physicality is their ability to withstand both heat and cold, having worked both in the depths of the freezing underground and near the blazing hellfire of the Grand Forges. No matter if they are in a tundra or desert, the Tantetsu clan member is able to regulate their inner body temperature to match the requirements of the environment and do not suffer from naturally-occurring frostbite or heat-stroke. As such, they feel everything at a constant temperature, with the exception of extreme circumstances, such as instances where they would be burned or frozen alive.
The ability to bend and mold steel into a potent blade is a rather under-appreciated skill, especially among shinobi. However, there are no better forge-masters in Iwagakure than the Tantetsu, who use their massive underground Grand Forges to construct weapons, armor, anything they are commissioned to do with not only the utmost speed, but the utmost skill also. While other clans are known for producing great and powerful blades, the Tantetsu clan blades are noted for their unique construction and forging, able to withstand pressures much too high for a regular blade.
By pouring their chakra into a blade while it's being forged and using certain materials, the creator can bestow it with a great number of different properties. Anything from a sword that glows in the dark, to a gigantic hammer that felt as light as a feather to the person bonded to it. Smithing is everything to the Tantetsu. They live for the task of creating and lament when such weapons find their way into use by those with whom they do not belong. Some even go out of their way to track down the clan's most ancient creations throughout history and retrieve them as relics; a grand inquisition to return these creations to their rightful owners.