Kenjaku’s “son” is Yuji Itadori from Jujutsu Kaisen.

Quick answer

In the story, Kenjaku refers to Yuji as his son because Kenjaku took over Yuji’s mother’s body (Kaori Itadori) and then gave birth to Yuji, making Yuji both biologically and metaphorically Kenjaku’s child within the series’ logic.

How Yuji is Kenjaku’s son

  • Kenjaku is an ancient sorcerer who survives by transplanting his brain into other people’s bodies and using them as hosts.
  • At some point, Kenjaku possessed Kaori Itadori’s body (Yuji’s mother) and, in that body, carried and gave birth to Yuji.
  • Because of that, fans and characters describe Yuji as Kenjaku’s son, and Kenjaku himself calls Yuji his son in the story.

Forum discussions often stress that this doesn’t mean Kenjaku has any parental love for Yuji; he mainly sees Yuji as a successful experiment and tool, similar to how he treats the Cursed Womb: Death Painting brothers.

Any other “Kenjaku’s son”?

  • Officially, the clearly confirmed “son” is Yuji Itadori.
  • There are fan theories and articles speculating about a possible “other son” of Kenjaku who might appear late in the story as a backup plan, but this is treated as theory, not hard canon.

So, for “who is Kenjaku’s son,” the solid, story-confirmed answer right now is Yuji Itadori.

Information gathered from public forums or data available on the internet and portrayed here.