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The Summoning Technique is a space–time ninjutsu that allows the summoner to transport animals or people across long distances instantly and uses blood as a sacrifice.
Before an animal summoning can be performed, a prospective summoner must first sign a contract with a given species. The contract comes in the form of a scroll, on which the contractor uses their own blood to sign their name and place their fingerprints and once signed it is valid even after the contractors death as long as the contract itself remains intact. After this, they need only offer an additional donation of blood on the hand they signed the contract with, mould their chakra with hand seals and then plant the hand they signed the contract with at the location they wish to summon the creature. The amount of chakra used during the summoning determines how powerful the summoned creature can be. It is possible for a summoner to summon a group of the same contracted animal, as opposed to a single individual.
It should be noted that anyone can summon a contracted animal as long as they have the blood of someone who has made a contract, the seal of the summoned creature and a source of sufficient chakra that the summon will accept. A creature is capable of determining who is attempting to summon it from the chakra used.
While most summoners have only been shown capable of summoning one type of creature, Nagato (through the Animal Path) was able to summon several different animals and even people, and seemingly did not require a blood offering when performing this technique. Sasuke is able to summon both snakes and hawks, though he has never been seen summoning both species at the same time.
Animals that are being controlled or tailed beasts or possibly a combination of both require the summoner's chakra to keep them under the summoning technique. If the user is forced to fight, the time limit will be further reduced and thus, they would not want to drag out a fight. Minato himself noted even an individual as powerful as Madara is unable to keep a being as powerful as Nine Tailed Demon Fox under summoned for a prolonged period.
When a summoning technique is being used, it's activation is marked by the appearance of formations of technique formulae (術式, jutsu-shiki), Kanji, Hindi script, or else other kinds of symbols (likewise with Fūinjutsu).
In the anime, it was shown that if a user attempts to summon an animal without first signing a contract, the user will be teleported to the home of the animal they have a natural affinity for. However, in the Boruto anime, when Boruto attempted to use the technique without a contract, it simply failed.
However in Boruto's case, he neither used a blood sacrifice nor did the necessary hand seals.
It's currently unknown if someone without the Animal Path can summon two different species of animal at the same time.
In the anime, it is shown that if the summoning contract is destroyed, the summoned creature would return to its home. It is also this particular summon managed to stay for 50 years after its master died, and only returned when the scroll is gone.