Soteijutsu

Sōteijutsu (装丁術, literally meaning: Binding Techniques) are a type of jutsu that seal inanimate objects (usually weapons) to a part of the body via a contract. These items can be later summoned. Simply put, sōteijutsu is like a combination of fūinjutsu and summoning techniques. It uses the properties of sealing one object within another, together with the properties space-time ninjutsu to create this technique.

Usage
Similar to creating a contract with an animal, the user signs a contract with the object. They first draw blood from their non-dominant hand and smear this onto the weapon being held in their dominant hand, followed by signing the contract, with their name and fingerprints. Also like summoning techniques, the contract continues even after the user's death as long as it is still intact. When the contract is signed, the weapon 'melts' down and infuses or coats the bones of the arm that the item is being held in. A burn scar shows up on the inside of their wrist, like one would for sealing an item into a scroll (ie '水' if water was stored.). All that's needed is a small sample of blood from the hand that signed the contract, molding their chakra with hand seals and to swipe the blood over the scar. This then summons the weapon, but as their limb, since it is still bound to the bones.

Trivia

 * This technique was created an perfected by the Akiyama clan, over many generations. With the eradication of their clan -- aside from Ōkami and Kasumi -- the art is nearly lost.
 * Releasing the summon is called sōteijutsu dissipation (装丁術解, Sōteijutsu Kai).
 * All members of the Akiyama clan learned the mechanics of the jutsu, even if they weren't to use it.