There are rumors circulating that Shin Uchiha from Boruto ( or Shinden) is actually Shisui Uchiha or Shishui’s son. We will take a look at the plausibility of both the theories and then try to draw an acceptable conclusion.
Is Shin Uchiha Really Shisui Uchiha?
First let us look as to why this idea seemed to interest fans. It is known that Shisui’s body was never recovered. While there was a general consensus that Shisui destroyed his body so that other shinobi won’t be able to take advantage of it, there were many who believed that Shisui managed to fake his death and survived out there in some form.
This belief has led many to question the true identity of Shin Uchiha. Also his obsession with Itachi Uchiha, who was Shisui’s best friend, fuelled the conspiracy theories concocted by diehard fans.
Who is Shin Uchiha?
When Naruto and Sasuke trace the past of Shin Uchiha, they end up talking to Orochimaru, who tells them that Shin Uchiha was once his test subject. He possessed a unique genetic structure which allowed his body to accept any type of tissue and cell transplants, including organs and limbs.
It was Shin Uchiha’s hand that was harvested ( the creepy one with multiple Sharingan eyeballs) and given to Danzo Shimura by Orochimaru.
At some point while he was still a test subject, he began developing a fixation on the Uchiha clan, especially Itachi (c’mon now, who wouldn’t be a Itachi fanboy, can’t blame poor Shin). His fixation grew to such a point that he even adopted the Uchiha name. Sometime later, he left Orochimaru and took with him most of the clones that were developed from his body.
His ideology was that peace was detrimental to human beings and hence he wanted to revive the Akatsuki, believing it was what Itachi would have wanted.
Why Shin can’t be Shisui
Let us now consider the possibilities. The theory holds water if we assume that Shisui’s body was recovered by Orochimaru and then experimented. However, there is a huge difference in the personality of both the characters.
Some fans point out that Shisui was angry that Itachi was killed by Sasuke and hence the change in behaviour. However, Shisui very well knew the path that Itachi would be forced to take after his death, and therefore would have understood why he made Sasuke go through all that trouble and kill his elder brother. Plus, he is someone who dealt with things in a peaceful way, and was a very humble shinobi. None of Shin’s traits match that.
If Shin were Shisui, he would have reminisced about his moments with Itachi while he was dying at the end of his arc (an emotional scene which most of the major villains and characters got). However we see no such flashbacks to support this theory and hence this possibility seems far fetched.
Was Shin Uchiha Shisui’s Son?
Again, it would mean that after losing both eyes, and jumping into the river, he managed to survive, marry and have a boy, who was then kidnapped by Orochimaru, converted into some kind of a mutated creepy person. This boy would then became obsessed with Itachi Uchiha and all the actions in the arc would follow.
This too seems very far-fetched and no evidence is available in the arc that supports this.
Also it has been passingly mentioned that Shin was raised by Orochimaru, meaning Orochimaru could have developed (or conceived) Shin and then raised him, ruling out all of his connections to Shisui Uchiha.
When the Shin arc ended, there was no evidence whatsoever that he was connected to Shisui. Shin was just a Itachi fanboy who went crazy. Consider the fact that the Shin Arc in the manga was actually a shinden, more like a spinoff short story which explored the relations between Sarada, Sakura and Sasuke.
There is nothing to support that Kishimoto would bring back a hero kind of character to be butchered in a sorry way, without even imparting any important lessons or viewpoints to the surviving protagonists or other characters. No, it doesn’t seem like him at all.
So I guess it is safe to assume at this point that Shisui Uchiha was not Shin Uchiha, and neither was Shisui Shin’s father.