Oborozuki (朧月, Literally meaning: Hazy Moon) is a Doujutsu-type Kekkei Genkai found in the clan Oborozuki and its numerous branches. It is rumored to have been connected to the moon itself, and clan members' eyes seem to take the form of the moon's phases as the Kekkei Genkai manifests. As a clan member progresses in strength, they begin to unlock greater 'phases' which seem to represent waxing in the left eye, and waning in the right. Each time a new level is reached, the user is granted new Jutsu, as well as an increase in ocular prowess.
There have been many confirmed methods of both achieving and evolving Oborozuki. The first, and most common method, is when a clansman experiences a powerful need or desire to gain power. This causes the brain to release a special form of Chakra that affects the optic nerve, transforming their eyes into Oborozuki. Less conventional methods of obtaining Oborozuki include simply reaching a level of power that it manifests naturally, or in numerous cases with children in the clan, knowing it well enough to force its activation. There has also been a single case in which Oborozuki was given to one who had no connections to the bloodline whatsoever.
Oborozuki first appears in the form of two crescent moons, waxing in the left eye and waning in the right. As the user becomes more skilled and/or powerful, the moons become able to expand to quarter moons, then gibbous, and finally full or new moons. Both the light and the dark sides of the moon give the user power, but the darker side (Yin Chakra) was lost to the clan long ago because of those who chose to follow the route they considered more powerful. Now, there are few clansmen who even know of the New Moon, or any of the Genjutsu abilities offered by Oborozuki.
Each form of Oborozuki grants the user both ocular prowess and techniques, but with this comes a change in the balance of the user's Yin and Yang Chakras. A little-known secret to the Kekkei Genkai is that the Jutsu it grants, once unlocked, are usable in any form that provides the necessary Chakra Nature (Yang for Ninjutsu, Yin for Genjutsu), and using the Jutsu with a phase more suited to the nature can make even the weakest ability in one's arsenal a powerful obstacle to overcome.
The crescent moon phase draws out the user's Chakra in a manner that yields 75% Yin Chakra, and only 25% Yang. This makes the crescent phase ideal for Genjutsu. Its Genjutsu is second only to that of the New Moon, but its Ninjutsu can only be considered reputable in the hands of a very skilled user. At this level, The user is capable of seeing Chakra by color. This allows a distinction between individuals, through transformations and the like. Additionally, when Chakra is molded into an elemental form, the color shifts. Raiton appears as purple, Katon as red, Fuuton as green, Doton as brown, Suiton as blue. This ability also proves useful when combating Ninjutsu, as the exact amount of Chakra may be seen, and matched with an equally, or more powerful Jutsu. Such methods are however, only effective when the user is capable of producing enough Chakra to match or exceed the opponent's.
The quarter moon phase amplifies the user's Yin and Yang Chakra equally, providing the most balance of all standard Oborozuki. At this level, the user is able to lock-on to an individual Chakra signature. While the Kekkei Genkai remains active at this level, only the source of the targeted Chakra is seen in color, whereas everything else appears in gray-scale. If the targeted Chakra is divided via clones or other methods, the vividness of its color lessens (i.e. if clones are used, the clone will appear less vivid than the original body, Shadow Clones being an exception due to the equal splitting of Chakra). Taking advantage of the ability to lock-on to a specific Chakra source, the user is able to 'mark' that which has been targeted via touch. This will connect the user's Chakra with the target's, causing Ninjutsu to hone in on the opponent, forcing said opponent into defending instead of evading.
The gibbous moon is the polar opposite of the crescent, providing 75% Yang Chakra and only 25% Yin Chakra. It is the penultimate standard moon for Ninjutsu practitioners. The user is able to sense specific Chakra signatures that come within a certain radius of his/her body, ranging from five to one hundred meters depending on the user's ability. Unlike the previous perception ability, this allows the user to know exactly where an opponent is, even without looking in their direction.
The full moon is the ultimate state of Oborozuki for use of Ninjutsu. It offers the user a 100% boost to all Ninjutsu at the cost of abandoning all Genjutsu abilities of the Kekkei Genkai. No further perceptive abilities are added by this state, but what it lacks in perception is made up for by Yang chakra being passively channeled through the user's body in high amounts. This can be likened to the activation of the Eight Gates in terms of its boost to all physical abilities.
The new moon is the ultimate state of Oborozuki for use of Genjutsu. While it offers nothing physical to the user, it grants a 100% increase to all Genjutsu-related abilities. Even a user who does not practice Genjutsu becomes able to create form from nothing, without relying on the typical restriction of Genjutsu that is having to affect the recipients' chakra flow. In a sense, this allows the user to create "real" illusions based on their imagination, which opponents cannot overcome the way they would normal Genjutsu.