Kamui

Kamui is a powerful Mangekyō Sharingan dōjutsu that creates a unique and specialised form of space–time ninjutsu. It allows the user to achieve two very distinct, yet closely associated feats — teleportation and intangibility.

Overview
Kamui allows the user to transfer targets to and from another dimension, from which they are unable to escape. Kakashi likened the characteristics of this technique to those of the Flying Thunder God Technique, but noted that it seems to be more advanced, as it requires neither seals nor a summoning tattoo to be performed. Minato Namikaze admitted that this technique exceeds both his and the Second Hokage's space–time ninjutsu.

Usage
This technique forms a spiraling void centred on the eye used to activate it, which draws the target inwards and distorts their form until they are transported to another dimension. By absorbing their own body into this distortion, the user can teleport to virtually any location they desire. When using Kamui to teleport, anything the user is touching will be warped along with them, and their chakra becomes untraceable. This technique was fast enough to avoid an attack from Naruto Uzumaki in his Nine-Tails Chakra Mode, though slower than the speed at which the Truth-Seeking Balls travel.

After storing a target within Kamui's dimension, the user can then eject it from their eye at any time. This can be done with varying degrees of force, allowing the user to eject weapons at a moment's notice, giving opponents little opportunity to react accordingly. Despite not always being present, Obito could keep targets under genjutsu while they were confined inside Kamui's dimension, thus keeping them incapacitated for extended durations.

Kamui can synchronise with another space–time ninjutsu, granting the user access to the synchronised technique's dimension, as well as any other connected dimensions. Once the dimension has been marked, the user can freely travel between it and Kamui's own dimension.

Left Eye
Obito's left eye is able to utilise a long-range version of Kamui, which can transport targets anywhere in the user's line of sight. The target is surrounded with a barrier space, the location and size of which can be specified at will, and when the user concentrates on the target within, the space at the barrier's centre distorts and draws everything within into another dimension. The size of the barrier can be expanded, as Deidara was forced to fly further away in an effort to escape its effects.

Right Eye
Obito's right eye uses a short-range version of Kamui, which can only transport targets in close proximity to the user; physical contact with the target is seemingly required. However, this eye can utilise a unique variation of teleportation akin to intangibility. When activated, any part of the user's body that overlaps with another object is seamlessly warped to Kamui's dimension, making it appear as though the user can phase through solid objects. By overlapping their entire body, the user can completely conceal their presence and erase all traces of their chakra. This also allows the user to freely travel through the ground, enabling them to ambush opponents from below. This intangibility can be extended to anything the user is touching at the moment of activation, so long as they are able to maintain physical contact with at least a portion of the desired object. This ability also allows the user to bypass even the strongest barrier ninjutsu.

Both Eyes
When both eyes are used together on the same target, the teleportation process works twice as fast. Through both eyes, the user can create two distortions at the same time and connect them. This was demonstrated when Obito first used the left eye's Kamui to synchronise with Yomotsu Hirasaka, then used the right eye's Kamui to teleport through the portal into another dimension. The user is also able to create portals in their line of sight to connect two dimensions. Using both eyes in conjunction with the Six Paths Chakra allows the user to augment their other techniques, transporting targets struck by said techniques to Kamui's dimension.

Drawbacks
As this technique is shared by two eyes, a user of one eye can counter a user of the other, making it useless to use Kamui against one another directly. The right eye can extend this negation to targets outside of the user's own body, as Obito negated Kakashi's attempt to decapitate the Demonic Statue of the Outer Path. Even if they are succesfully transported to Kamui's dimension, a user of this technique can simply teleport back out, provided they have enough chakra to do so.

The Mangekyō Sharingan is a dōjutsu that, with continuous usage, burdens the user with the loss of their eyesight. Since this is the source of Kamui, using it in rapid succession put Kakashi's body at risk as well. As his eye was received through a transplant, the strain on Kakashi's body was even more severe than an Uchiha would suffer, and repeated use of Kamui was shown to cause his eye to bleed. Kakashi was originally only able to use this technique three times before being rendered immobile, and his aim and control over the size of the barrier were imperfect. Over time his aim and control improved, as he was able to accurately warp away small and fast moving objects, such as a nail. After further improving, he was capable of transporting a target as large as the Demonic Statue's head, though doing so required time to prepare the necessary chakra. After receiving chakra from Kurama, Kakashi was able to quickly transport a target as large as Gyūki to the other dimension and later eject the tailed beast from his eye, as well as utilise Kamui more times than he would usually be capable of. He estimated that the influence of Kurama's chakra, when given directly by Kurama, made his usage of Kamui at least three times more powerful than usual.

The right eye's primary weakness is that the user must solidify in order to utilise Kamui's teleportation, resulting in a brief period in which they are vulnerable. This deficiency means that the user must also materialise when ejecting stored items, presenting the same vulnerability. Additionally, the sections of the user's body residing in Kamui's dimension can still interact normally with anything inside said dimension, meaning the user can be damaged by such items. Obito could only maintain his intangibility for approximately five minutes at a time, and it took him longer to absorb himself than another person or object. After becoming the Ten-Tails' jinchūriki, Obito discovered that he could no longer use Kamui to pass through objects. Madara was able to transport himself to and from Kamui's dimension as the Ten-Tails' jinchūriki using Obito's left eye, establishing that some aspects of the technique still function.

Using Kamui to synchronise with another space–time ninjutsu requires an immense amount of chakra. Additionally, creating portals between separate dimensions, particularly those that are far apart, places a significant amount of strain on the user's eyes, causing them to bleed.

Influence
Kamui is the word for a divine being in Ainu mythology, although it is almost never written with kanji in modern times. In a more general Japanese context, Kamui refers to the might and majesty of the gods, particularly the Shintō Kami.

Trivia

 * Unlike other Mangekyō Sharingan users, Obito's continuous usage of Kamui does not seem to cause his eyesight to deteriorate. Kakashi, however, claimed he lost most of the vision in his left eye.
 * In Road to Ninja: Naruto the Movie, The Creation of the Akatsuki, and several anime episodes, Obito is depicted using Kamui without activating his Mangekyō Sharingan.
 * There are instances in the anime where Obito transports targets to Kamui's dimension without establishing physical contact with them. Similarly, in the manga, he seemingly transports Sakura Haruno out of Kamui's dimension without touching her.
 * With his Sharingan, Shin Uchiha can make use of a Space–Time Ninjutsu that, in function, is virtually similar to this technique.