The Mangekyou Sharingan – Kaleidoscope Copy Wheel Eye – is the evolved state of the Sharingan, the kekkei genkai of the Uchiha Clan.

When activated, their eyes transform into a unique pattern rather than the tomoe of the original doujutsu. This evolution is capable of all of the Sharingan’s innate abilities such as the Eye of Insight and Eye of Hypnosis but elevates their power, improving the clarity of their vision and the realism of their illusions.

Each Mangekyou favours one of these abilities over the other depending on the wielder’s talents and compatibility. Those who are most compatible with the Eye of Insight are known as straight tomoe, granting fluidity to their movement as their perception allows them to better evade and counter their enemy. And those most compatible with the Eye of Hypnosis are known as curved tomoe, granting more detail to their chakra sight and further empowering their genjutsu.

Most importantly, the Mangekyou Sharingan grants its wielder powerful jutsu that makes them far more dangerous than the typical Uchiha. Jutsu that would take decades for an ordinary ninja to try and create themselves and would likely still fall short.

Jutsu that can create black flames that burn for seven days and nights, control one’s perception of space and time, dominate the victim’s mind without their knowledge, teleport themselves and others to a unique subspace or create a guardian spirit of chakra.

These jutsu vary from individual to individual and there is no way to control which ones they gain. Some say that they get the jutsu that best suits their life experiences while others say that it is decided from birth but the true answer is a mystery. The total number of these jutsu is finite and it has been known for more than Uchiha to have the same jutsu as another even generations apart. However some jutsu are rarer than others and the specifics of these jutsu can vary between individuals even when they are technically the same.

Each eye has its own jutsu but this too can vary. These jutsu may be entirely different from one another, complementary to one another, exactly the same as one another or even have the same jutsu but with different aspects of their power expressed in each eye.

And an unusual trait of these jutsu – even among kekkei genkai – is that the wielder does not name them. As the Uchiha explores them and their understanding grows, the name of the jutsu is instinctively imparted to them just like how they know how to perform the jutsu in the first place.

Awakening the Mangekyou Sharingan

Among the small number of Uchiha who have acquired the Sharingan, even fewer of those have met the conditions needed for the Mangekyou Sharingan.

Where the Sharingan is awakened by the Uchiha experiencing strong emotions, even greater extremes are needed to awaken the Mangekyou Sharingan.

To acquire it, one needs to have already awakened the Sharingan. Then they must directly experience the loss of losing a loved one by witnessing their death. If the depth of their grief and sorrow is deep enough – overcoming even the emotional conditioning and calloused heart of a shinobi – it triggers a reaction within their doujutsu to elevate it the next stage of evolution. Even if the Sharingan had not yet fully matured, it automatically does so upon awakening the Mangekyou Sharingan.

The origins of this evolution lie with the progenitor of the clan, Otsutsuki Indra, who was born with the Sharingan but discovered that he possessed even greater ocular powers later in life. He found that he could further transform his eyes and through which he could unleash a variety of powerful jutsu. These abilities were passed down to his descendants but were buried so deeply in their bloodline that the triggers needed weren’t discovered until centuries after Indra’s lifetime.

Thus the first to awaken the Mangekyou Sharingan were the brothers Uchiha Madara and Uchiha Izuna.

A lifetime of war had weakened the mind of their father and the leader of their clan, Uchiha Tajima. He lived longer than most shinobi in that era and remained a powerful one, but his ever-growing mental instability caused him to make mistakes that fractured the clan’s strength and was ultimately leading them to ruin.

So to save the clan from that destruction, together the brothers killed their own father.

But the love and respect they had for their father made this act one of emotional torture that served as a trigger for their doujutsu’s evolution. Together, they named this power the Mangekyou Sharingan which they used to unite the clan with Madara as their new leader.

Once the rest of the Uchiha learned how they awakened it, more than a few became desperate to possess it themselves. And the only way to awaken the power by choice instead of chance was to willingly kill someone they loved. By killing a loved one, it forces them to not only experience the pain of their death but combines it with the guilty of causing that death in the first place which practically guarantees the awakening of the Mangekyou Sharingan.

It became a ugly secret among the Uchiha that one who has acquired the Mangekyou Sharingan is one that may have murdered a friend for it. But that was merely the price of power.

Controlling the Tailed Beasts

The Sharingan has the potential to control the Tailed Beasts.

Ordinary genjutsu have proven unable to affect the Tailed Beasts as ninja are not capable of manipulating their immense and powerful chakra with their own. But the origin of the Sharingan’s ability gives it a unique connection with the beasts to influence them.

Only those with the most powerful, fully mastered Sharingan are capable of using its power on the Tailed Beasts and they would only be able to suppress a portion of their strength to weaken them. Given the rarity of such mastery, as well as the sheer destruction the beasts would inflict on those foolish enough to fight them, the ability was practically unknown for centuries.

But by awakening the Mangekyou Sharingan, that potential is realized in full. Even without using the evolved doujutsu itself, they are able to dominate the Tailed Beast to bend them to their will.

Even Jinchuuriki are not immune as the Sharingan can still perceive the Tailed Beast within their host and influence them with its power. And while a Jinchuuriki and Tailed Beast cooperating can free one another from a Sharingan’s genjutsu, if both of them are hypnotised then they become as vulnerable to control as anyone else.

Uchiha Madara proved this incredible power to the world after he abandoned Konohagakure when he found the Nine-Tailed Fox, the most powerful Tailed Beast, and controlled it with his Sharingan to fight against Senju Hashirama in a legendary battle.

Afterwards, the Uchiha edited the stone tablet passed down in their clan to show those with the Sharingan how to achieve its evolution as the possibilities of such power were too tempting to ignore.

Cost of the Mangekyou Sharingan

The price exacted from possessing the Mangekyou Sharingan is blindness and the more one uses the eyes then the faster they lose their eyesight.

Each time one of its jutsu is cast, it causes a physical backlash upon that eye which damages their nerves, vessels and delicate components. In the immediate sense, this results in the wielder suffering intense pain and even increasingly worse bleeding from that eye but long term this has the permanent effect of weakening their vision. Over time, they experience episodes of disorienting double vision and their eyesight becomes increasingly dim and blurry – even with the Sharingan’s supernatural acuity – until they cannot see anything.

If one never used the Mangekyou Sharingan, it would take decades to go blind. But anyone who awakens this power is unlikely to ever avoid using it if needed. The rate at which the eyes lose their vision depends on how many times they are used and how often they are used. But using it too many times too quickly means suffering the greater pain than usual and their vision deteriorates at a faster rate as well. But by carefully conserving the use of their jutsu, they can preserve their sight and skills for years if not decades.

Medical ninjutsu and medicine are only able to heal the short-term effects to reduce inflammation and bleeding but the damage to their eyesight is permanent, immune to repair even by the most skilled of medical ninja.

There are only two known ways to overcome the Mangekyou Sharingan’s cost.

One is the cells and chakra of Senju Hashirama because of the powerful life force and regenerative ability of his unique body. By implanting his cells into their body, one becomes almost entirely immune to the damaging effects of the evolved doujutsu which allows them to perform as many of its jutsu as they desire without losing their eyesight.

The second is to make the Mangekyou Sharingan eternal.

Eternal Mangekyou Sharingan

An eternal Mangekyou Sharingan is one that can never lose its light and could be called the last stage of the doujutsu.

This can only be achieved by a Uchiha replacing their Mangekyou Sharingan with the eyes of a direct blood relative – such as a sibling, parent or offspring – who has also achieved Mangekyou Sharingan. If their compatibility is great enough, the host’s chakra mixes with the donor’s chakra in the transplanted eyes to trigger another transformation. This merge is reflected in the new pattern of the eyes which are a combination of the host and donor’s original ones.

Those with an eternal Mangekyou Sharingan possess all the powers of their original eyes and their vision is permanently restored.

The doujutsu’s abilities are actually no more powerful than before. However, using the eyes in their previous state was painful and the consequences meant that it needed to be done sparingly; they could not be practiced like ordinary jutsu and had to be tested in live combat instead. Now that the only cost is chakra, the wielder can train and experiment with their doujutsu as much as they need without losing focus. While the eyes can still bleed in response to channelling such power, it does not cause them any pain or lasting harm which makes it far easier for the Uchiha to draw out their doujutsu’s true potential.

Unlike the instantaneous awakening of the Sharingan and the Mangekyou Sharingan, awakening an eternal Mangekyou Sharingan is a gradual process as the eyes recover from the transplant and mix the respective chakras together over time. If the eyes aren’t compatible with the new host then they are instead stuck with whatever abilities and remaining eyesight those tranplants possess.

The only two people to have ever awakened an eternal Mangekyou Sharingan are Uchiha Madara and Uchiha Sasuke.

In his numerous battles against Senju Clan, Madara had nearly lost his eyesight from overusing the Mangekyou Sharingan. As his younger brother lay dying from their last battle with the Senju, Izuna offered his less damaged eyes to Madara so that he could continue protecting the Uchiha Clan in his absence. Madara tore out his own eyes and replaced them with his brother’s, unknowingly starting the transformation that made his Mangekyou Sharingan eternal.

Those who followed in the brothers’ footsteps and awakened the Mangekyou Sharingan themselves tried to achieve this as well but continually failed. With there only being a single precedent – and the exact circumstances involved weren’t something that Madara shared with his brethren – Uchiha would steal the eyes of their own clansmen in the hopes of awakening the Eternal Mangekyou Sharingan only to fail continually. It was only through trial and error that they came to the conclusion that it would only work with a direct blood relative who had awakened the Mangkeyou Sharingan themselves.

But awakening the Mangekyou Sharingan became less common over the generations; the initial craze for its power fading and the Uchiha placing strict control over one another. It became a rare thing but those who did possess its power were still respected among the clan for said power.