Principal Masamichi Yaga was killed in Jujutsu Kaisen because the higher‑ups in jujutsu society ordered his execution after the Shibuya Incident, seeing him as a traitor and a threat due to his knowledge of advanced cursed‑corpse creation.

Why the higher‑ups wanted him dead

  • After Shibuya, the elders marked Gojo, Yuji, and Yaga for death, believing they were responsible for the chaos.
  • Yaga was imprisoned and interrogated because he alone knew how to create fully independent cursed corpses like Panda, which the elders wanted to control.

How he actually died

  • After being freed by Kusakabe, Yaga was tracked down and executed by Yoshinobu Gakuganji , who carried out the elders’ order.
  • Even while dying, Yaga refused to sell his secret cheaply; instead, he passed the cursed‑corpse formula to Gakuganji , calling it a “curse” he was handing on rather than a gift.

Story and thematic reasons

  • Yaga’s death wraps up a major thread from the Shibuya Incident and shows how the old‑guard elders will sacrifice even powerful allies for control.
  • It also deepens Panda’s arc, since Panda is literally Yaga’s creation and now must live with the legacy of that “curse.”

If you want, I can break down how this ties into current manga events or what fans are speculating about Yaga’s research in 2026.