Shinobi

, also interchangeably referred to as, are the primary focus and the main military power in the series. A female ninja is known as a. Most come from a hidden village, of which some come from specialised ninja clans, and will perform missions for a fee. These missions can include: doing manual labour, acting as escorts, gathering secret information, retrieving stolen items, carrying out assassinations, etc. In times of war, ninja will come together to defend their villages and land. The clearest characteristic of a shinobi is their ability to manipulate chakra to create and use techniques. Shinobi are expected to be loyal to their villages for life, and any defectors are considered to be missing-nin, and will be marked for death.

History
The origins of the ninja ultimately date back over a millenia to the arrival of Isshiki and Kaguya of the Ōtsutsuki Clan, celestial invaders who sought to cultivate a God Tree and harvest a chakra fruit on Earth. After Kaguya fell in love with a human and betrayed her clan, she passed the power of chakra on to her twin sons, Hagoromo and Hamura. Kaguya was eventually driven to madness and battled against her own sons, who sealed her away and divided her chakra into the nine Tailed Beasts. In time the elder brother, Hagoromo, would develop the philosophy of ninshū, through which he sought to disseminate chakra among the human population as a means of uniting them in harmony, and became known as the Sage of Six Paths.

It was Hagoromo's elder son, Indra, who first developed methods to weaponise chakra, creating ninjutsu. Following Hagoromo's death a feud erupted between Indra and his younger brother Asura for leadership of the sect, spurred on by a being known as Zetsu, bringing about a multi-generational conflict that would divide its followers into various clans and engulf much of the world for centuries. During the resulting Warring States Period, Hagoromo's teachings were gradually forgotten until all that remained of ninshū was ninjutsu, and those who wielded the techniques became known as ninja.

Two of Hagoromo's descendants, Hashirama Senju and Madara Uchiha, would eventually unify a number of clans to found Konohagakure and form an alliance with the Land of Fire, resulting in the first of the Five Great Shinobi Countries and the modern shinobi village system, in which various unified clans act as mercenary forces for affiliated nations. Though this resulted in brief periods of peace, large scale conflict still plagued the world for several consecutive generations, resulting in the First, Second, Third, and Fourth Shinobi World Wars.

During the Fourth Shinobi World War the Five Great Shinobi Countries came together to form the Allied Shinobi Forces and battle the Akatsuki, an organisation that had been manipulated by Zetsu in order to gather the Tailed Beasts and revive Kaguya and the God Tree, using it to place the world under the Infinite Tsukuyomi, a mass hallucination. The heroes of the war, chief amongst them being another pair of Hagoromo's distant descendants, Naruto Uzumaki and Sasuke Uchiha, put an end to Zetsu's plots and once again sealed Kaguya, beginning an era of unprecedented peace and cooperation between the shinobi villages.

In the following decades the villages prospered under the leadership of Naruto and other like-minded shinobi who prioritised unification and sought to end the cycle of war. This era was marked by rapid scientific advances, with the marriage of technology and ninjutsu resulting in the creation of Scientific Ninja Tools and Shinobi-Ware. However, underlying societal unrest and inequality gave rise to the Kara, a secret society of zealots and dissidents devoted to the Ōtsutsuki Clan and the God Tree. With the sudden arrival of another pair of Ōtsutsuki invaders, the Kara plunged the world into a conflict that would soon end the era of the shinobi.

Jutsu
Shinobi can use a variety of techniques often based on the utilisation of chakra. This allows shinobi to perform extraordinary feats such as walking on water or walking up trees. Jutsu are separated into three groups, ninjutsu, genjutsu, and taijutsu. Ninjutsu implies performing a supernatural or beyond normal ability, the most common of which is the elemental jutsu. These are created by the user transforming their chakra into a specific nature or 'release'. The chakra types are Lightning, Earth, Fire, Wind, and Water. Other sub-types of chakra natures such as Wood Release and Ice Release also exist, created by combining two of the basic five releases. Taijutsu implies physical body techniques, which do not typically require chakra. Genjutsu manipulates the chakra in an enemy's brain and disrupts their chakra flow. Their senses get fooled which creates illusions, things that the foe believes to be real that are in fact fake.

Physical Prowess
Shinobi have noticeably greater physical capabilities than a normal human being, able to execute feats of strength that would be otherwise impossible for a civilian, even at relatively low levels of skill. For example, their ability to jump. Ninja are capable of leaping many times their own height and permitting them to clear buildings and structures, especially when moving across rooftops or travelling through trees. Even as a boy, Naruto jumped over a fence in the Academy with no significant effort, and each of the pre-Academy children in Himawari's test trial could easily move at great speeds and jump up dozens of feet in the air. Near the start of his battle against Sasuke Uchiha at the end of Part I, Naruto jumped from the Hashirama Senju statue to the Madara Uchiha statue, reaching the other end of the entire valley in just one leap. However, moments like these are greatly ignored and overlooked due to the fact that they are so commonplace in the ninja world, even for genin-level shinobi. Ninja also possess strength that far outmatches the average person. A simple kick from Itachi to Sasuke created an exceptionally large crater in the wall. With a single hand, Lee could uproot the roots of giant trees in a flash without apparent difficulty.

Befitting their occupation, shinobi possess superhuman speed to varying degrees. Some exceptional genin can avoid attacks moving at the speed of sound, or physically intercept them with their own attack at a faster speed. At some point between his adolescence and young adulthood, Kakashi is said to have bisected a bolt of lightning with his Chidori. These and other notable instances aside, nearly all shinobi can temporarily heighten their speed to catch opponents off guard or to set a decoy.

Mental Prowess
Though not greatly explored, shinobi also possess abnormal abilities to affect the minds of others, even without the use of genjutsu or other Yin Release techniques. Without using techniques, shinobi can induce intense panic and suicidal tendencies in those less experienced or weaker than themselves by projecting their Killing Intent. Skilled use of it can even take the form of graphic hallucinations of one's own death, which can be mistaken for genjutsu.

Tools
Ninja tools are used as alternatives to techniques. They can include weapons, accessories, and even clothing. Some ninja such as Tenten have mastered the use of such tools, but all ninja are able to use the most common to some degree. A standard shinobi will have a pouch equipped with many tools, and nearly every ninja is equipped with at least a shuriken holster. Most also possess and wear a forehead protector with the symbol of the village they derive from, though the ninja does not necessarily have to wear it over their forehead. The Inuzuka clan's ninken and Aburame clan's insects are also classified as tools.

Scientific Ninja Tools
During the new era, the marriage of technology and ninjutsu results in the creation of various scientific ninja tools. These range from weapons and equipment utilising modern materials and technology to devices that can store and reproduce the phenomena of ninjutsu, and even cybernetic Shinobi-Ware that can augment the abilities of their wielder.

Trivia

 * The compound kanji means "endure" and is comprised of the kanji for  and, with the literal meaning of "heart under blade".  literally means "people who endure", while  is a shortened form of , a native kun'yomi pronunciation of the same phrase, "people who endure".
 * The true meaning behind the word is mentioned several times throughout the series by the likes of Jiraiya, Hashirama Senju, and Naruto Uzumaki. In the final epilogue narrated by Sasuke Uchiha, he states that ninja are those burdened with the task of enduring hardships for the sake of a greater cause, in particular bringing about peace through unification.
 * is derived from the three individual strokes in the kanji for, and originates from the so-called used specifically by female ninja. The term was not commonly used during the Edo era, but was popularised as shorthand for a "female ninja" in the 1960s through the works of fiction author Futaro Yamada.