WARNING: The following contains spoilers for the Boruto: Naruto Next Generations anime, Episode 100: "The Predestined Path."
Throughout the annals of modern Japanese manga and anime, there are few villains with the poise and impact Orochimaru has had on the Naruto franchise. He's done it all -- been a legendary Sannin ninja, turned on Konoha and his people, manipulated weapons of mass destruction like Sasuke, and helped bring about endless wars, both on his own and with the terrorist organization called the Akatsuki.
But it's his stealthiest act that's leaving a lasting legacy, one we're seeing unraveling in the Boruto anime presently: His sinister science experiments. And while he's no longer cut from this villainous cloth, it seems someone new has picked up this aspect of Orochimaru's game.
The last three Boruto episodes have seen the titular character (and Naruto's son) journey outside Konoha to a nearby river village, only to find a plague sweeping towards his home. Cursed Seals (aka marks that turn people and animals into mindless, overpowered zombies) are spreading like a virus. Boruto's team have come to the realization that it's being carried by birds and the waters surrounding the area, the first hint that a new Orochimaru was in town. After all, the snake-master loved to experiment with these marks in his Naruto stories.
It gets even worse as Boruto's allies discover this new enemy has found a way to weaponize the ritualistic marks, turning rogue ninja kids into weapons. Shockingly, this time they actually have full control of their actions, which means the Cursed Seals are power-ups, like steroids, enhancing warriors at the push of a button on an electronic collar. That's a red flag, too, because Orochimaru has become just as versed in technology as he is in medicine, evolving with the scientific times.
The only issue is, Orochimaru has been redeemed since the end of the last Great Ninja War, and has been under the watchful eye of Konoha. To top that off, his new research is helping create a better world, and he also sent his offspring Mitsuki to be Boruto's right-hand man. So there's no way he's doing this, despite his obsession with the marks in the past.
Now, that's not to say his technology couldn't have been stolen or repurposed without him knowing it. After all, Kabuto (his former apprentice) was famous for this theft, especially when the wannabe-Orochimaru revived the real Uchiha Madara and almost brought about the apocalypse a decade or so ago. Kabuto could have been a contender as well in this case, but he was also redeemed, helping Naruto and Sasuke save the world and unite the ninja villages. He's also helping orphans in this new era, so it's unlikely Kabuto has regressed to his evil ways.
As it stands, apart from a brand-new player on the board, the only other option is Kara, the shady terrorist cell Koji Kashin works for. We know they're involved with engineering on a whole new level, as shown by the creation of Kawaki. Something like this -- creating child soldiers and using chemical warfare -- is right up their alley.
Until more clues emerge, all we can say is, there's another Orochimaru rising. And until Boruto uncovers answers, these Cursed Seals are bringing back destructive characters like Jugo (Naruto's version of the Incredible Hulk and one of Orochimaru's prized possessions) to possibly incite another big war. We don't know what other weapons this unseen enemy has in store as well, so this risky predicament may require Boruto to call in his father to ensure the past doesn't come back to bite them and leave a mark they all can't ever recover from.