Gaining the Mangekyo Sharingan is an achievement that is enough to raise a shinobi far above their Uchiha peers, and the select few who have awakened it throughout history went on to become legendary figures in both Konohagakure and the shinobi world. In addition to the standard abilities of the three-tomoe Sharingan, the Mangekyo Sharingan also grants unique powers which vary between individuals, apparent in the different pinwheel-style tomoe that define its appearance. Among the Mangekyo Sharingan abilities possessed by characters in Naruto, few are as overwhelmingly powerful as Obito Uchiha's Kamui. Portrayed as a form of space-time ninjutsu rooted in a specific dimensional plane, Kamui was a signature of Obito's fighting style, which relied on the intangibility and teleportation powers he was able to employ with his Mangekyo Sharingan.
Even taking on extremely powerful shinobi in Naruto was not a stretch for Obito, who became a major threat to the Five Great Shinobi Countries on reaching adulthood and mastering his use of Kamui. The right half of his body, which was cultured from Hashirama Senju's cells, is theorized to be the reason behind his capacity to repeatedly use Kamui at all times with no loss of vision — a sharp contrast to Kakashi who struggled to handle the huge drain it imposed on his chakra reserves. Over the course of the story he fought the likes of the Fourth Hokage Minato Namikaze, as well as jinchuriki such as Naruto Uzumaki and Killer B to a stalemate, defeated some of Root's most skilled shinobi, and a large part of the Uchiha clan during the night of the massacre. When examining his earlier development prior to awakening the Mangekyo Sharingan, there is a stark difference in ability when Kamui comes into the picture. Considering the feats Obito has performed during his lifetime, it is worth inquiring into the excessive power up this ability granted him and how it affected the power scaling throughout the series.
The Power Of Intangibility
Obito's right eye, which was his only source of Kamui for most of the series — after gifting his left eye to Kakashi — allowed him to transport objects or individuals at a short range into Kamui's dimension. Although he is often shown to be in physical contact with the target, this condition did not remain consistent in every instance, indicating that it is not entirely necessary. On activating this technique, a spiraling void appears to emanate from Obito's eye, slowly warping the appearance of his target until it is completely sucked into the dimension. After entering Kamui's dimension, the objects or people cannot be sensed from the outside world and become entirely untraceable. Some view it to be superior to Minato's Flying Thunder God, although the actual combat applications of both techniques diverge quite a lot.
More often than not, Obito is shown using this ability to transport himself between dimensions, either to traverse long distances instantly, or to escape attacks he cannot defend against. This comes full circle when applied to grant him intangibility, where specific body parts are automatically transported to Kamui's dimension. Everything that Obito is in contact with, including clothes, weapons, and opponents pass through him seamlessly, giving off the impression of intangibility. Obito sneak underground and surprise opponents with the aid of Kamui, which is one of its most pertinent offensive abilities. He has used this ability to evade Minato's Flying Thunder God, Konan's Paper Shuriken, attacks by Fu and Torune of Konohagakure's Root, as well as the Five Kage, illuminating how much of an unfair advantage this ability granted him. Where most shinobi would need years of training to match the speed, strength, and variety of jutsu thrown at them, Kamui allowed Obito to sidestep them all effortlessly. This also played into his persona as Tobi, where he would feign incompetence and weakness, yet still emerge unscathed from any attacks thrown at him.
Instantaneous Teleportation
Alternatively, Obito's left eye, which was in Kakashi's possession for much of Naruto, allowed him to perform a long range version of the technique, although his own proficiency at it was far more limited due to his limited chakra reserves and the fact the was not from the Uchiha clan. In this case, Kakashi could create a similar spiraling portal at a point of his choosing, which would drag anything caught within its range into Kamui's dimension. This ability was first used during his pursuit of Deidara during the Kazekage Rescue Mission, where he was able to transport the Akatsuki member's arm into Kamui's dimension. Kakashi initially struggled with maintaining its accuracy and was left visibly drained after using it in quick succession. Over time, his command over the technique evolved to a point where he was able to teleport away rapidly moving nails launched at him and Choji by Pain.
When combined with the right eye, these two ocular powers are some of the most versatile techniques seen in the Naruto universe, where Obito became one of the strongest shinobi of his generation relying on them alone. In fact, he seldom used the innumerable other jutsu in his arsenal, primarily due to how effective Kamui was against opponents at all levels. It could be used against extremely strong opponents in any sort of combat situation, dealing with short or wide-ranging attacks, or even aid in taking on swarms of opponents at once without taking any damage from their combined assault. This is likely one of Kamui's greatest benefits, far outweighing its few weaknesses and drawbacks when placed in the hands of an able and astute user such as Obito. Furthermore, even with intangibility alone, Obito could drag out fights for long enough to ascertain an enemy's weaknesses and strike decisively before they were able to comprehend the true nature of his visual prowess.
The Only Point Of Weakness
Compared to the several incredible advantages it granted, Kamui's weaknesses were quite limited, and the biggest chink in its armor lay in the fact that Obito had given his left eye to Kakashi. Hence, Kakashi was a natural countermeasure against Obito's seemingly overpowered dojutsu, where he could enter Kamui's dimension and deal damage to the parts of his body that had been transported there for the purpose of rendering him intangible. Kakashi could also transport himself between the two dimensions at will, negating Obito's measure of teleporting away when the odds were stacked against him. This relationship set up the fated confrontation between the two inside Kamui's dimension during the Fourth Shinobi World War, which ended with Kakashi destroying the Cursed Seal on Obito's heart with his Lightning Cutter.
Besides this, one of Kamui's only other weaknesses came from how long Obito could keep it activated. At its limit, Obito could keep Kamui active for a maximum of five minutes, a fact that Konan attempted to take advantage of during her fight with Obito. In this situation, Obito was forced to use Izanagi to sidestep this weakness, although it seldom proved to be a problem for him when looking at how he constantly made use of his Mangekyo Sharingan ability. Additionally, since the actions of teleportation and intangibility were linked, he could not perform both simultaneously, leaving him unable to flee while on the defensive. Finally, he was also vulnerable during the moments before he attacked, where he had to become tangible once again — a narrow window that Minato exploited with his Flying Thunder God - Second Step. All in all, Kamui was a formidable power in the hands of a shinobi of Obito's level, and maybe even the most overpowered of all the Mangekyo Sharingan abilities in Naruto, with few, if any shortcomings. Its potency allowed Obito to perform his role and move in the shadows, manipulating the Akatsuki to see out the Eye of the Moon Plan.