WARNING: The following contains major spoilers for Boruto: Naruto Next Generations #46, by Masashi Kishimoto, Mikio Ikemoto and Ukyo Kodachi, available in English from Viz Media.
One of the most intriguing aspects of the Boruto manga is the mystery surrounding the Kara soldier, Kashin Koji. When he refused to kill anyone from Konoha upon confronting Boruto's crew in the past, it was odd because Kara usually deploys deadly assassins. It got weirder still when he then snuck into the Land of Fire and past the security chakra barriers, which led us to think he was actually Jiraiya (Naruto's godfather), as only someone from Konoha could do that.
Following the release of Boruto #46, this speculation has intensified due to the familiar combat style as employs as he turns on his leader, Jigen. But at this point, the manga needs to stop with this teasing as it's frankly getting annoying. More importantly, it's also detracting from his purpose: stopping Jigen's designs on world-conquest as Isshiki Ōtsutsuki.
Jiraiya remains a beloved character as he mentored Naruto's dad, Minato, as well as Naruto himself. He died in battle against Pain and the Akatsuki, but the role he played in Naruto's formative years shaped the kid's destiny as Hokage. Fans were sad he didn't get to see what Naruto and Sasuke became but it was a warrior's death and the sacrifice ultimately helped Konoha unite all other villages to take down Obito and Madara.
It seemed to be a definitive death when Pain stabbed him with chakra rods in the Land of Rain and dropped him to the bottom of the sea. Jiraiya never returned in the series which is why it was a big deal when the hints started dropping that he might be Koji. Doubters felt he was slimmer and more somber than Jiraiya, but the grey hair and the chakra barrier angle certainly had theorists plugging away.
Naysayers might not be able to argue after Chapter #46, "True Identity," however, as we see Koji using fire blasts, shadow clones and toad oil tricks to increase the temperature of his flames, and also, summoning fire from the Flaming Mountains to burn his opponent. Knowing Jigen can't absorb real fire as it's not a jutsu (i.e. chakra-generated) is the kind of strategy Jiraiya uses, and when Koji uses the mud swamp jutsu to turn the ground beneath Jigen's feet into a murky weapon to trap him, you can't help but think he really is the Ero Sennin in the flesh, reborn.
These are some of Jiraiya's signature moves, not to mention toads are his summoning creatures. He also confirms he's a shinobi and as Naruto watches the brawl through a spy toad that's transmitting to Konoha thanks to the defector, Amado, he's stunned. He whispers about Koji reminding him of someone but doesn't finish the train of thought.
As cool as that is, it's also really exasperating because, at this point, we'd just like to know for sure whether or not Jiraiya has been reborn, or if he's one of Amado's clones/science experiments. We can't see him surviving Pain's attack and staying off the radar for so long, but the more speculation mounts, it detracts from his purpose to end Jigen's reign. It also wouldn't do the book justice because if he is Jiraiya, fans might get annoyed it took so long to get the obvious out in the open, and the reveal would lack impact later down the line. The trigger needs to be pulled now as stringing people along for so long feels cheap.
Conversely, if Koji isn't Jiraiya then fans might be even more ticked off because it'd feel like the series tried too hard to swerve them with misdirection. Whether it's a straightforward twist or a bait-and-switch, people will likely losing interest. It also feels like the manga is forcing Koji to be an important character, but just by betraying Jigen, he already is one. To do him justice, it's best to reveal exactly what his origin story is and why he was a secret hero all along rather than piggybacking on a conspiracy theory.