WARNING: The following contains spoilers for Boruto: Naruto Next Generations Episode 173, "The Secret Behind The Underground Room," now streaming on Crunchyroll.
The Boruto anime has been slowly filling in Kara's backstory with key pieces of narrative not yet revealed in the manga. Viewers are learning more about the civil war within the terrorist cell through Victor and Deepa, and about the group's secret labs meant to study scientific items like the Hashirama Cell. However, in the latest episode, one of the manga's biggest mysteries may have just been solved thanks to Konohamaru and Mugino infiltrating Victor's medical facility in the Land of Valleys.
Boruto Chapter 35 showed Jigen, who didn't harness his form as Isshiki Ōtsutsuki just yet, teleporting to a secret dimension where he held a monster captive. As Sasuke spied, it turned out to be the Ten Tails, the creature Naruto and the alliance fought when Kaguya tried to enslave humanity and bleed their chakra dry. This was all so the Ten Tails could transform from a seedling into the God Tree, giving her chakra fruit to feed on and evolve. That plan was foiled and Kaguya was sealed away after fusing with the creature, leaving the husk behind.
With the Ten Tails gone, fans were wondering how Isshiki could have one in his possession. Many wondered if the seedling beast could have been brought to Earth with him and Kaguya, which would have consumed his female colleague, thus giving Ishhiki fruit to eat. However, while that's yet to be clarified, Victor may have the answer for its reappearance as Konohamaru and Mugino discover he's been growing a smaller version of the God Tree.
This is what he's been using Hashirama's DNA for, as the First Hokage has the closest genetics to this tree. Victor has been feeding it workers so the tree actually expands its roots to try to devour the Konoha shinobi and Victor's shady doctor, indicating it's sentient just like the older models. Now, if Victor has a tree, chances are he could have reversed engineer it to produce the foundation it sprouted from -- a Ten Tails. Isshiki is known for not needing perfect specimens, after all, and with his knowledge, plus Hashirama's DNA and any cells from the husk from Naruto, then they could easily have been cooking up the beasts and trees in Kara's labs.
As it stands, one may have been perfected and this is what Jigen stored away so he could feed himself to it, be reborn in Kawaki's body and then come to eat the fruit. Notably, Kara seems to be adept at chakra experiments so this may well have created a Ten Tails as close to perfect as possible if their work with the Hashirama Cell has been extensive and successful. That said, what's quite clear is with Victor's expertise and a God Tree, Isshiki always had the tools for his mission nearby.