Full Story Of Itachi and Shisui Camaraderie

When you think of iconic duos in Naruto, you think of Naruto and Sasuke, Madara and Obito, Kakashi and Might Guy. But the duo of Itachi and Shisui was the one that was very short-lived.

Itachi and Shisui were one of the more iconic duos because of how well their fighting styles complemented each other, but if you only watched the Naruto Shippuden anime, you are probably unaware of the true story of how Itachi met and what truly served as the foundation for the relationship.
The relationship didn't start out as the two of them as clan members who automatically became best friends forever, but instead, like a lot of friendships in Naruto, they started as two rivals.

How they met

Itachi became a very good genjitsu user, not just because his father was a genjitsu specialist. In the days when Itachi's baby Sasuke was born, he threw himself headfirst into training because he saw that he would one day be expected to be a shinobi, and if there was a war going on in the ninja world, Sasuke might be expected to die for his village, like the way that those dead shinobi Itachi saw when fugaku took him to the battlefield.
 
Itachi began training like a madman, perfecting the hidden shuriken Justu of the Uchiha clan main branch. Itachi was then interrupted by Shisui, who praised Itachi for being so adept at shuriken Justu despite him being young and not having a sharingan.
 
Shisui then shows off his complex shuriken Justu techniques with the aid of his sharingan. This left Itachi jealous, making him work even harder, and he even got eager to awaken his own sharingan.
Itachi Having seen his father use the sharingan,he knew that the sharingan was the fastest way to gain the power he needed to rise through the ranks of Konoha.
 
Itachi's first encounter with Shisui led them to train together, especially when Itachi isn't training with his mother or father and also when Shisui isn't on any missions.
 
The sparring matches between the two were so intense, but Shisui would always come out on top without the aid of the sharingan.

 
Shisui Awakening His Mangekyo Sharingan

Shisui went on a mission to retrieve dead bodies on an island. One of the dead bodies on the island happened to be the corpse of his former teammate, which made him emotional and in turn led to the awakening of his Mangekyo Sharingan. Ever since then, he has been watching Itachi Train, helping him hone his skills in order to improve so that they could work together as teammates.
It turns out that watching The Itachi Train helped Shisui with his grieving. 

 
Itachi Becoming a Ninja

After the nine-tails attack, the training became more intense as Itachi became a genina and started going on missions. After Itachi experienced a tragedy of his own, he also awakened the sharingan, which led Shisui to focus more on training Itachi. After fugaku, Itachi's dad trains Itachi, and Shisui will then help Itachi hone his genjitsu skills.
 
Danzo gave Itachi permission to choose a teammate for the mission, and Itachi turned down Fugaku's offer, telling him to go to Sasuke's academy or he would attend the ceremony instead and throw off the mission. For Itachi, Shisui was the obvious choice for the mission.
 
They were sent on a mission where they encountered Mukai, a half-Hyuga rogue anbu of high skill who pushed Itachi and Shisui to their breaking point in the battle before he was eventually killed.
 
Before the massacre takes place, Shisui will continue to mentor Itachi but also openly tease him about a certain half-blooded uchiha who seemed to always be around Itachi and constantly looking for him when they were apart, and she was someone that Itachi was spending a growing amount of time with during his free time. When he was training with Shisui or wasn't on anbu duty, Shisui teased Itachi, catching feelings for his girlfriend, Izumi. At times, he struck a nerve with his teasing.
 
However, as we all know, it wasn't all smiles forever; both Itachi and Shisui were well aware of what was going on with the uchiha, having attended the meeting and seen how the fugaku had lost control of the clan and had given in to the cause of a Coupe de tat. This led to Shisui reporting to Hiruzen and playing a double agent, while Danzo made Itachi a double agent for himself.

How Did Danzo Get Shisui's Eye So Easily? 

Shisui was poisoned by an aburame anbu whose insects were so small that only Itachi could see them when he was made aware of their presence, and he was using the Mangekyo Sharingan. The poison was moving throughout his body; hence, Shisui tore out his remaining eye and died in front of Itachi to ensure that Itachi
I awakened the Mangekyo Sharingan.