Tengen

Tengen (天元), often referred to as Master Tengen (天元様) is a supporting character in Jujutsu Kaisen. They are an immortal jujutsu sorcerer that remains within their chamber; the Tombs of the Star Corridor at all times in order to reinforce the barriers that protect both Jujutsu High locations.

Master Tengen is also known as the "Star" (星). They were responsible for preaching the foundation of jujutsu sorcerers and spawning religious groups that worship the Star as their deity.

Appearance
Due to the nature of Tengen's role in the jujutsu world, most people have no idea what they look like. Only those granted permission have seen that Tengen does not quite possess the appearance of a typical human being. Tengen has four eyes with a cylinder-shaped head that features no hair at all, but they do possess a bipedal humanoid body. They wear a simple light-colored robe.

As stated by Tengen, due to Toji Fushiguro killing the previous Star Plasma Vessel 11-years ago and unable to fuse with her, Tengen's current appearance is the result of him having continued to "evolve" past his humanity. This in turn implied that Tengen himself originally possessed a much more human appearance.

Personality
Tengen appears to be a well-mannered, straightforward, and knowledgeable individual with humanity's best interest in mind. They don't seem to mind awkward questions about their experience and is more than happy to help normal jujutsu sorcerers provided the right situation.

Tengen was willing to do all they could to help Yuji and the others stop Kenjaku, but in return asked that two members of his team remain behind to protect them as well. They were stern about this point, but only because Tengen's own safety is the key to humanity's survival.

History
During the Nara Period, Master Tengen spread Japanese Buddhism and preached what would become the foundation for jujutsu sorcerers.

Gojo's Past Arc
In the modern age Master Tengen does not interact with the outside world. They use a barrier technique to protect both jujutsu schools and to strengthen all of the auxiliary managers barrier techniques. Their immortality cursed technique must be reset once their body reaches a certain age. The technique will attempt to change bodies, forcibly evolving Tengen to a higher state, losing their will and potentially making them an enemy to humanity.

In order to prevent this, every five hundred years, Master Tengen must merge with a compatible star plasma vessel to rewrite their body's information. Once the body is refreshed, the cursed technique will be reset as well. In 2006, the Star Plasma Vessel was Riko Amanai.

Two groups targeted the girl; the curse user group Q who aimed to overturn the jujutsu world by having Tengen lose all reason, and the Time Vessel Association, the star religious group that worshipped Tengen as their deity. In order to ensure Riko's safety, Master Tengen had Masamichi Yaga assign his students Satoru Gojo and Suguru Geto with escorting the girl to Jujutsu High before the merger on the full moon.

Riko is ultimately assassinated by Toji Fushiguro who was contracted by the Time Vessel Association to kill the girl and prevent the impure merger. Even so, Master Tengen was somehow able to stabilize according to Yuki Tsukumo.

Culling Game Arc
When Yuki along with Yuji, Megumi, Maki, Yuta and Choso enter the shrine and find nothing. Yuta tells them to leave because Tsumiki doesn't have time, however, just then Master Tengen appears in front of them and greets them all. Yuki confronts Tengen, asking aren't they going to say hello to her while Tengen replies that it wasn't the first time that they've met. Yuki asks why they closed off the Tombs of the Star Corridor where they reveal that they were afraid they were aligned with Kenjaku, someone who Yuki doesn't recognizes and asks who they are. Tengen reveals that Kenjaku was the sorcerer who was once Noritoshi Kamo but now has inhabited Suguru Geto's body. Yuji suddenly interrupts the conversation and asks why Tengen looks the way they do who says that although they're immortal, they aren't immune to aging. They also add that in 500 years, he will look the same way as they are which surprises Yuji.

Tengen then explains Kenjaku's true method for forcibly evolving humanity, which is to merge humankind with Tengen themself. They go on to explain that over the past 11 years, after the failed merger with the Star Plasma Vessel, they have evolved to the point in which it is not impossible for them to merge with entities that are not Star Plasma Vessels. Furthermore, this evolution has made their soul become "the world itself", making Tengen more cursed spirit than human being. For this reason, Tengen requests that two people out of Choso, Yuki and Yuta stay behind to protect them from Kenjaku, to which Yuki and Choso volunteer. In return, they reveal the key to unsealing Satoru Gojo: the "back gate" of the Prison Realm. However, the two cursed tools required to "break through", the Inverted Spear of Heaven and the Black Rope, were both destroyed by Gojo himself 11 years and one year ago, respectively. Tengen then reveals the only other way to forcibly free Gojo from the Realm: through the cursed technique of an ancient sorcerer, Hana Kurusu, which can extinguish any cursed technique.

Abilities
Overall Skill Level: While Tengen does not interact with the outside world or go on missions, their abilities have been essential to protecting the pillars of the jujutsu world for thousands of years.