Kamui

Overview
Kamui is a space–time ninjutsu that can be used with Ougi Uchiha's Mangekyō Sharingan.

Kamui allows the user to transfer objects to and from another dimension. These transfers are often characterized by a spiralling void that targets swirl into or out of, distorting their form as they move between dimensions. Targets that enter Kamui's dimension are completely untraceable, as not even their chakra can be detected while they're there. Targets that exit Kamui's dimension do so with varying force, either simply appearing at the ejection point or flying from it; if weapons, such as shuriken, are stored in Kamui's dimension, ejecting them forcefully gives Kamui's users an offensive option.

Using Kamui is the only way to travel to and from its dimension. This means that targets transferred there are trapped, forced to stay until Kamui's user lets them leave; Kagami sometimes uses genjutsu on those he imprisons to keep them subdued. This also makes Kamui's dimension effective as a refuge, as anyone taking shelter there can only be reached by using Kamui. Because Ougi's two Mangekyō Sharingan were seperated, her right and left eye are immune to eachother.

Kamui ordinarily only connects its dimension with the Earth. If a user synchronizes Kamui with another space–time ninjutsu, Kamui can travel to the other ninjutsu's target dimension. But if the user doesn't have the original ninjutsu to piggyback off of, travelling between dimensions becomes extremely difficult since Kamui doesn't naturally connect to them. Users can manually generate portals to these other dimensions with Kamui, but this requires a great deal of chakra, so much that users will likely need another person's assistance. Additionally, Ougi in the Purgatory is able to use Kamui to temporarily return her soul to Earth to continue assisting Kagami by granting him the use of her Sharingan for a short time.

Right Eye
With Ougi's right Mangekyō, a short-range version of Kamui is used. Ougi most often uses this version on herself, sucking herself into his right eye to enter Kamui's dimension and then exiting back to whatever location she pleases. Sometimes she does this in order to escape attacks, other times she does this in order to travel long distances. Ougi can perform this teleportation at will and doesn't need to designate his destination beforehand, leading others to label it superior to the Flying Thunder God Technique. Others can be sucked into Kamui's dimension through his eye in addition to or instead of Ougi, and in fact it is faster for her to use Kamui on others than on herself. Ougi is usually shown requiring physical contact with those she's using Kamui on, but this isn't always consistent.

Ougi can also use the right Mangekyō to temporarily transfer all or parts of her body to Kamui's dimension. Her body (and anything she's holding) will remain visible to others, but they won't be able to interact with her. Ougi often uses this ability defensively, transferring her body to Kamui's dimension so that attacks will harmlessly pass through her. Alternatively, Ougi can make her entire body intangible, whether to pass through barriers or other obstacles, or to travel underground and surprise opponents with attacks from below. Ougi can only keep her body intangible like this for approximately five minutes, and so long as even part of her is intangible she is unable to use Kamui to teleport; in the brief moment between when she solidifies and when she teleports, Ougi is vulnerable. Alternatively, opponents can circumvent her intangibility by transferring themselves or their attacks to Kamui's dimension, which will enable them to damage whichever body parts she's currently keeping there.

When Kagami is a-hold of both of Ougi's Mangekyo, he is able to use these techniques, in exchange for a huge amount of chakra. Later, when he fights Yasad Uzumaki and Genesis Uzumaki, he uses the phasing technique to counteract their attacks, but he was later taken care of with Genesis's Flying Thunder God technique, and Yasad's self-repelled Rasengan.

Left Eye
With Ougi's left Mangekyō, a long-range version of Kamui is used. The user looks at a target and creates a "barrier space" around them, with the barrier's size being determined by the user. When the user concentrates, anything within the barrier is pulled towards its centre, transferring the target to Kamui's dimension. When Kagamii first begins using this version of Kamui, he struggles to perform it with any accuracy, frequently missing his target. Even if he does hit his target, he has difficulty making the barrier space large enough to pull the entire target in. In time, he becomes accurate enough to teleport projectiles mid-flight, and later can make the barrier space large enough to teleport the Demonic Statue of the Outer Path's head. Kagami eventually learns to create the barrier around himself, allowing him to teleport just as Ougi does.

Because Kagami is not the original owner of the eye, using Kamui demands a great deal of chakra for him to perform. It takes him an extended period of time to gather enough chakra to use it, and once he does he can only use it so many times before his chakra is depleted; originally his limit is three times in a day, but this is later increased to an unspecified number. Similarly, because Kamui is used with a Mangekyō Sharingan, repeated use damages Kagami's vision, eventually reaching the point where it causes his eyes to bleed. When Kagami receives his Kagune Release, he is able to use Kamui faster, more often, and on targets as large as the Baryonyx; he estimates that the Kagune Realease's chakra makes Kamui three times more powerful than usual.

Both Eyes
When both eyes' Kamui are used on the same target, whether by a single user or two users working together, the teleportation speed is doubled. Alternatively, two Kamui can be generated separately to achieve a unified purpose: Ougi uses the left Kamui to synchronize with Rodgetta Tomioka, then uses the right Kamui to teleport to its associated dimension. With the two Mangekyō, users can also perform Susanoo, through which they can create Kamui Shuriken.