Master Tengen has finally been revealed. They are willing to provide information on the identity of Pseudo-Geto and on how to unseal Satoru Gojo. However, Tengen requires that some of the group stay behind in the Tomb as security. When the question of how the life of an immortal being can be threatened is raised, Tengen reveals the fate-altering consequences of the incident eleven years ago.
While everyone else is surprised by Tengen's appearance, Yuki asks why Tengen didn't address her in their greeting. Tengen replies this isn't the first time they've met. Yuki's next question is why the Tombs of the Star Corridor was closed off. Unable to see into the human heart, Tengen feared Yuki could've been in alignment with "Kenjaku".
Kenjaku is the name of the body-switching entity that was once Noritoshi Kamo and now inhabits the body of Suguru Geto. Yuji cuts in on the important conversation to ask why Tengen looks so strange. Megumi quietly thinks to himself that Yuji has guts for doing so. Tengen explains that despite their cursed technique provides immortality not anti-aging. Eleven years ago a new Plasma Vessel failed to appear, so Tengen's aging process accelerated, and their self-awareness as an individual diminished. They were forced to evolve and have become one with the world itself.
Megumi and Yuta get to the point and ask about Kenjaku's objectives and how to unseal Gojo from Prison Realm. Tengen will provide the information on one condition, at least two of the three people present that are ranked special grade must remain at the Tomb to serve as Tengen's guards. Willing to provide more information first, Tengen explains that Kenjaku wants to force the evolution of all the people of Japan. He can't do so using Tengen's barrier with Idle Transfiguration because that requires massive amounts of cursed energy. Triggering an evolution of that scale using a cursed technique is inefficient.
The method Kenjaku has chosen to force evolution on a massive scale is to merge Tengen with mankind. Since progressing into a new state, it is possible for Tengen to merge with someone who isn't the Star Plasma Vessel. A human who merges with Tengen evolves into something beyond a sorcerer that is both there and not a part of the physical realm. Tengen stabilized and can maintain self-control even after evolving thanks to barrier techniques, but the world would end if mankind reached this state. There would be no boundaries between individuals and the impurities of millions of humans would flood the world. What happened to Tokyo would engulf the entire planet. Tengen cannot refuse the merger because their evolution has caused them to become more cursed spirit than human being, a perfect target for Cursed Spirit Manipulation.
Due to the threat of Kenjaku coming to unseal the Tomb, the corridor is rejecting everyone that approaches. Kenjaku was the one who set the plan into motion that stopped the merger eleven years ago. They were involved with Sukuna over a thousand years ago so Yuki wonders why he's just now making a move. Apparently, Tengen, the Star Plasma Vessel, and the Six Eyes are connected by "fate". Kenjaku was defeated by two Six Eyes users is in the past. After his second defeat, Kenjaku killed the Star Plasma Vessel and the next Six Eyes user soon after they were born. Despite his efforts, they both appeared on the day of the merger with Tengen anway. This made him switch to the method of sealing the Six Eyes instead of attempting to eradicate it.
However, the unexpected occurred eleven years ago when Toji Fushiguro intervened. He was a man who escaped cursed energy and therefore was not bound by the chains of fate that affect the jujutsu world. In effect, Toji destroyed the destinies of Tenge, the Star Plasma Vessel, and the Six Eyes. Along with him came Suguru Geto, a boy who could manipulate cursed spirits. Once Kenjaku secured Prison Realm six years ago, all his plans fell into place.
The Culling Game is a ritual to prepare the people of Japan for the merger. It uses the players' cursed energy and the barriers to convey everyone "to the other side". Through this custom, Tengen can be forced to merge with humankind. In order to pull off something of this level, Kenjaku has restricted himself with binding vows. One vow stipulates that he is not the Culling Game's master, meaning killing him won't even the game. The Culling Game can only end once all the players are dead and there are rules in place to ensure nothing can interrupt the ritual. Yuji and the other's best course of action are to spend one hundred points to add rules where Tsumiki and other unwilling participants can escape the game. Freeing Satoru Gojo would also obviously be ideal. Before Tengen reveals how to do so, they require the group to pick a combination of Yuta, Yuki, and Choso to serve as guards.
Yuki and Choso volunteer themselves to protect Tengen. Choso knows Yuji will need Yuta or Yuki's help and this will also give him the chance to protect his brothers should Kenjaku come for Tengen. Yuki isn't finished talking to Tengen anyway and would like to stay if that's okay with Yuta. Wanting to remain with the other students, Yuta gleefully agrees.
After expressing their gratitude, Tengen takes out the "back" of Prison Realm, a separate cursed object that will be necessary for unsealing Satoru Gojo. It serves as the back gate for Prison Realm and was hidden by Tengen to try and conceal the existence of the front. Kenjaku found it anyway and he bears complete authority over Prison Realm as the bearer of the front gate. Breaking open the back would require cursed tools that can cancel cursed techniques, like the Inverted Spear of Heaven or the Black Rope. However, both of those were lost in separate battles with Satoru Gojo. Yuta searched for more Black Rope in Africa with Miguel to no avail.
There still remains one way to open the back gate of Prison Realm. A thousand years ago there was a female sorcerer who called herself an "angel". She possessed a cursed technique that can extinguish other cursed techniques. Her name is Hana Kurusu and she's been incarnated as a Culling Game player.