Shisui was noted to be one of the most talented members of the Uchiha clan (gaining the moniker of Shunshin no Shisui for his usage of the technique). During some point in his life, he fought with Ao of Kirigakure, who, to this day, still remembers Shisui's chakra signature and his ability to manipulate others through his Sharingan.
He was ordered by the Konoha Military Police Force to keep tabs on Itachi, who had begun to act strangely upon joining the ANBU. Some point later, his body was found in the Naka River, with a suicide note planted on him in his handwriting stating that he was tired of carrying the clan's duties.
Initially, the Uchiha clan suspected Itachi of murdering Shisui and forging his writing with the Sharingan, as Shisui was (apparently) a very devoted member of the clan, and such actions would have been very uncharateristic of him.
On the night of the Uchiha massacre, Itachi revealed to Sasuke that he had murdered Shisui (who he had considered his 'best friend') to obtain the Mangekyō Sharingan.
Recently, however, Itachi told the 'true' story of the incident. According to Itachi, Shisui was perplexed that the clan would not deter from the coup d'etat they were planning, and attempted to use Kotoamatsukami to stop them. This plan, however, never came to fruition as before it could happen, Danzō Shimura stole his right eye, admanat on doing things his own way.
Subsequently, out of fear that Danzō would get the left eye as well, he entrusted it to Itachi Uchiha, telling him to protect both the village and the Uchiha name. Afterwards, he would later make it appear as though he had crushed his own eyes, before disappearing without a trace (Kabuto noted that he couldn't find his body.)
According to his clan, Shisui was a devoted member of the Uchiha and very trusted. As a testament to this, the Konoha Military Police Force entrusted him the task of spying on Itachi, and it was because of this very devotion and trust the clan held for him that his 'suicide' aroused suspicion on Itachi.
His devotion to the clan, however, was not a match for his even greater devotion of protecting the village, where he was willing to go as far as casting a genjutsu on his entire clan to stop the coup d'etat and the potential consequences that may have followed.
Among other things, Shisui was also Itachi's best friend, and older brother figure, teaching him that "self sacrifice...a nameless shinobi who protects piece from within it's shadow" was the true mark of a shinobi, which would later become the very basis of Itachi's true character and philosophy.
Though we don't know much of him, the little that we've been told about Shisui indicates that he was a powerful shinobi and a great fighter. He was noted to be a talented member within the Uchiha clan (which is a feat in itself, considering that the clan is quite easily the strongest in the manga thus far). He had the nickname of 'Shunshin no Shisui', which implies a mastery of Shunshin no Jutsu - but much like his backstory, this was later retconned/forgotten for the Kotoamatsukami plotline. His abilities were as such that Kabuto wished to revive him with Edo Tensei, but lacked sufficient DNA samples for it. He may also have a high tolerance of pain or stamina, given that he had his right eye stolen by Danzō and later tore out his left eye as well to give to Itachi.
Shisui was among the few of his clan who unlocked the Mangekyō Sharingan. It is unique in that unlike Itachi and Sasuke's Mangekyō Sharingans (which granted them Tsukuyomi, Amaterasu and a unique Susano'o), it also (presumably had had access to the other three, or at least Tsukuyomi and Amaterasu) granted him Kotoamatsukami - perhaps the strongest genjutsu we've seen to date. The technique allowed him to enter the victim's mind, and plant false experiences in them, so that he could freely manipulate them while they were unaware that they were under the effects of an illusion.
The technique was highly sought after throughout the manga: Danzō stole an eye for himself, Tobi wished to obtain the eye he stole and Kabuto grew excited once he found out the left eye was hidden in Itachi's crow. However, the genjutsu does have a very strong limit - it's usable only once per decade, unless the user is able to gain the cells of Hashirama Senju (like Danzō did), in which case they're presumably able to use it once per day after reducing the cooldown.
Contradictions and QuestionsEdit
- If Shisui killed himself, then how did Itachi gain the Mangekyō Sharingan? Out of guilt?
- The Konoha Military Police Force came to Itachi's house, telling him that they found Shisui's body lying in the river. If they found a whole body, how did Kabuto not have access to sufficient DNA samples? He managed to revive Deidara, who blew himself up.