WARNING: The following article contains brief discussion of suicide and self-harm.
One of the biggest debates in the Naruto Universe has always been who's the most powerful Uchiha. It was thought to be Madara, but over time Sasuke proved just as strong, if not more so, by attaining the Rinnegan. Still, Itachi was better and had he not sacrificed his life to save his younger brother, many felt he'd have become a ninja even more powerful than Naruto with the way he manipulated his Sharingan eyes.
However, even Itachi wasn't as strong as his clan-mate, Shisui. Now, given the mystical and scientific arcs at play in Boruto, this sequel could bring him back and give Shisui a more complete, wholesome arc.
Itachi saw him as a brother, revering Shisui who was already a deadly ninja with the ABNU covert ops team. Shisui protected Konoha, with many enemies fearing his Body Flicker technique that felt like teleportation. Honestly, he was the closest shinobi the Hidden Leaf had to Naruto's father -- the Fourth Hokage, Minato.
Shisui's prowess and tactical mind became the stuff of legend despite him being so young. A lot of this had to do with his Mangekyō Sharingan, awakened when he saw a comrade die. It allowed him to trick people into dreams via genjutsu, probe minds and alter folks' wills. It's why Hiruzen, the Third Hokage, wanted to use him to mind-control the Uchiha to stop their thirst for civil war in Konoha.
Sadly, Danzō would take one of his eyes as he sought power, wanting to overthrow Konoha for himself. Shisui found Itachi and let him know about the Uchiha and Danzō, inspiring his protege to take up the mantle. Shisui committed suicide by jumping into the Naka River, while giving Itachi his final eye. This awakened Itachi's Mangekyō Sharingan, and he would pretend he killed Shisui so Sasuke would seek revenge and level up down the line.
Now, it's a tragic story for Shisui, but he could return given how Boruto has brought Jiraiya back. He was cloned by Amado and used as a Kara terrorist, but this Jiraiya, aka Kashin Koji, just wants to protect the land. Thus, seeing as Shisui's body was never found, Amado or some other science cell could have found him. He could have been cloned or maybe even kept alive all these years, as a blind shinobi with tons of wisdom. It would make him a hermit akin to the Sage of the Six Paths, and would provide an organic link to Naruto.
After all, Itachi was glad Naruto inherited Shisui's will to loyally defend the free world, so having the new Hokage, Boruto, Sasuke and Sarada meeting Shisui would change their lives forever. If it weren't for him, Itachi wouldn't have set them all down this road, so it'd definitely feel like they met the author of their destinies. This would also add tension as he endorsed killing off his clan, which would stir conversation with Sasuke and Sarada -- or even the Uchiha-esque outsider in Kawaki.
Interestingly, Kabuto tried to find Shisui's corpse and reanimate him during the Kaguya War when Kabuto was evil. He failed, but that doesn't mean some other shinobi can't use a mystical jutsu to find Shisui's soul. There are so many scrolls, spells and links to the Reaper around, and seeing as the likes of Madara and the Hokages were brought back, someone could have found a way to summon Shisui without his DNA.
Ultimately, should Shisui return to Konoha, he would get to see his dream in Boruto's peaceful utopia. It's what he, Itachi and Hiruzen always wanted. Madara and Obito couldn't let their hatred go, Itachi died and Sasuke wasn't leadership material, so this would allow Shisui to connect with Sarada's aspirations to be Hokage someday and help make her the Uchiha-leader or advisor Konoha never had.
For more information on the warning signs and prevention of suicide, click here. If you or someone you know is in emotional distress or considering suicide, call the National Suicide Prevention Lifeline at 1-800-273-TALK (8255). If you live outside the U.S., click here for a list of international hotlines.
