The Sharingan is an exclusive and unique ocular technique belonging solely to the Uchiha clan, renowned as one of the three great visual jutsu and a bloodline limit specific to this clan. The techniques derived from it are often named after characters from Japanese mythology. Within the Uchiha clan, emotions of love are sealed away, only to be released once a member comprehends love. However, due to the intense nature of their affection, there exists a potential for them to go berserk. When an Uchiha individual who has understood love loses that profound feeling or undergoes deep sadness and pain, a special chakra emerges within their brain. This particular chakra acts upon the optic nerve, resulting in a transformation of their eyes – known as the Sharingan – which serves as a reflection of their soul.

The power wielded by the Sharingan is intricately linked with one's soul strength, enabling rapid enhancement in physical abilities. It should be noted that the potency of its abilities corresponds directly with the darkness present within one's soul; thus indicating that individuals possessing darker souls possess stronger eye powers.

The First Stage: Normal Sharingan

The initial awakening stage for the Sharingan manifests as a one Tomoe.

Once activated into its Single Tomoe form, further improvement in ninja skills leads to its evolution into Double Tomoe (although there exist exceptional cases such as Uchiha Obito who awakens directly with Double Tomoe).

Upon activation into 2 Tomoe state and subsequent advancement in ninja capabilities, it progresses further into 3 Tomoe.

At this juncture, achieving three Tomoe represents attaining the highest evolutionary stage possible for normal Sharingan.

The Second Stage: Mangekyō Sharingan

The Mangekyō Sharingan is an advanced eye technique beyond the normal Sharingan.

To attain the Mangekyō Sharingan, one must:

1. Personally kill the person closest to them, as mentioned by Uchiha Itachi.
2. Witness the death of the person closest to them with their own eyes, such as Uchiha Sasuke and Uchiha Obito.

One of the above two conditions can be achieve Mangekyō Sharingan Eye.

Different ninjas manifest unique abilities based on their skills, resulting in the shape of the Sharingan eye also differently.

Here are some classicial Mangekyō Sharingan eyes:

Uchiha  Madara's Mangekyō Sharingan

Uchiha Kaguya's Mangekyō Sharingan

Uchiha Shisui's Mangekyō Sharingan

Uchiha Itachi's Mangekyō Sharingan

Uchiha Sasuke's Mangekyō Sharingan

According to Itachi Uchiha, when the Mangekyo Sharingan is turned on, it means losing eyesight. Although the Mangekyo Sharingan gives the caster powerful pupil power, each use will cause irreversible damage to the caster's body (eye bleeding, poor vision, unbearable body pain, etc.). Eventually, overuse can lead to blindness and death.

To avoid these negative effects of the Mangekyō Sharingan, there are only two choice:

1. Implant cells from the First Hokage, Senju Hashirama. This method minimizes the negative effects of the Mangekyō Sharingan, as seen in the case of Uchiha Obito.

2. Evolve into the Eternal Mangekyō Sharingan.

The Third Stage: Eternal Mangekyō Sharingan

The conditions for opening the eyes of the Eternal Mangekyo Sharingan will be more stringent: the Mangekyo Sharingan of an immediate relative must be transplanted (not the ordinary Sharingan). It takes a period of time for fusion after transplantation to open the Eternal Mangekyō Sharingan. Such as Uchiha Madara, and Uchiha Sasuke.

Uchiha Izuna's Eternal Mangekyō Sharingan

Uchiha Sasuke's Eternal Mangekyō Sharingan

At this stage, the Eternal Mangekyō Sharingan is the most advanced form of the Sharingan. After the Eternal Mangekyō Sharingan is activated, the negative effects are almost gone. When Uchiha Sasuke first activated the Eternal Mangekyō Sharingan, there was still some eye bleeding during jutsu use, but the pain has been greatly reduced. In the later stage, the negative effect of the Eternal Mangekyō Sharingan was almost reduced to zero.

Rinnegan

Above the Eternal Mangekyō Sharingan is the Rinnegan, considered the most powerful pupil jutsu, and is known as the "Eye that Controls Life and Death." The conditions for awakening the Rinnegan are even more demanding. Except for Otsutsuki Kaguya, Otsutsuki Hagoromo and other Otsutsuki clans, only Uchiha Madara and Uchiha Sasuke are unlocked by acquired conditions.

To activate the Rinnegan, all of the following conditions need to be met:

• Be in a near-death state.
• Fuse the chakra of the Sage of the Six Paths' sons, Asura and Indra, to awaken the power of the Six Paths.

 

Uchiha Madara bit off a piece of Hashirama's flesh during their final battle, transplanted it into his left chest, and waited until he was near death to awaken the Rinnegan.

Uchiha Sasuke during his battle with Uchiha Madara, entered a near-death state after being impaled by Madara's sword. Later, as the reincarnation of Hagoromo, he received the "Yin Power" of the Six Paths. His body was also implanted with cells from Hashirama Senju (possessing Asura's chakra) by Hagoromo, healing his wounds. Finally, Sasuke awakened the Rinnegan in his left eye, known as the Six Tomoe Rinnegan. When Sasuke overuses the Rinnegan, it temporarily reverts to a standard Rinnegan form. This allows him to retain the abilities of both the Mangekyō Sharingan and the Rinnegan.

Samsara Eternal Mangekyō Sharingan Rinnegan

The Eternal Mangekyō Rinnegan can only be awakened after becoming the Ten-Tails' Jinchuriki. The user can cast a colossal genjutsu known as the Infinite Tsukuyomi.

The Naruto anime shows that each evolution of the eye technique implies increasingly stringent activation conditions and an enhancement of visual abilities. Gaining power also means losing something in return.