A shocking theory has emerged in Jujutsu Kaisen: Modulo suggesting that Tengen might be an alien from the Simurian race, stranded on Earth and responsible for the foundation of jujutsu.
This idea closely resembles Naruto’s explanation of ninjutsu originating from the extraterrestrial Otsutsuki clan, sparking fans’ curiosity about the mysteries soon to be revealed.
1. A Simurian member mentioned that jujutsu sorcerers possess powers similar to theirs

The first clue appears in the opening chapter of Modulo, where a Simurian member states that jujutsu sorcerers in Japan have powers similar to theirs. This raises suspicion that Tengen, who laid the foundation for the jujutsu world, could be the first Simurian to arrive on Earth.
2. Tengen’s nickname is Star or Hoshi, hinting at an extraterrestrial origin

Tengen is also known by the nickname “Hoshi,” meaning “star” in Japanese. Not only jujutsu sorcerers but also his followers call him this. The nickname seems to imply that Tengen is not from Earth but came from outer space to establish the jujutsu world here.
3. Tengen’s mysterious physical condition

In Jujutsu Kaisen, Tengen possesses a cursed immortality technique and must merge with a Star Plasma Vessel every 500 years for two main reasons.
First, although his immortality technique allows him to live indefinitely, it cannot stop his body from aging. Every 500 years, his body evolves, and if he does not merge with the Star Plasma Vessel, he loses his humanity and becomes a dangerous entity that could threaten the entire jujutsu world.
Second, Tengen plays a crucial role in maintaining the barriers of jujutsu schools and protecting Japan from deadly curses. The merging process resets his technique, ensuring he retains enough power to carry out his duties steadily and safely.
This merging is not just a personal need but vital to preserving the balance of the jujutsu world. Could this condition exist because Tengen was never originally from Earth?
4. Jujutsu culture exists only in Japan

The concept of curses has existed alongside human history because it relates to individuals’ negative emotions. However, interestingly, only Japan seems to have a developed jujutsu culture. Most other countries do not appear to have such a complex tradition.
This might be explained by Tengen, a Simurian, arriving early on Earth and creating a jujutsu civilization similar to his homeland. This theory explains why some say the Simurian race and jujutsu sorcerers share similarities, much like ninjas and the Otsutsuki clan in Naruto both understand chakra.
Of course, this is just a theory. But perhaps we will discover the truth in upcoming developments of Jujutsu Kaisen: Modulo.