Choso calls Yuji “brother” because, in the story’s lore, they are effectively related through the same twisted parent figure, Kenjaku/Noritoshi Kamo, and Choso emotionally embraces that bond in a very literal way.

Why Does Choso Call Yuji “Brother”?

In-Story Explanation (Canon)

  • Choso and his “siblings” (Eso, Kechizu, and the other Cursed Womb: Death Paintings) were created using the experiments of Noritoshi Kamo, an identity of Kenjaku, who mixed human women with cursed objects to produce them.
  • Yuji Itadori is also tied to Kenjaku: Kenjaku possessed Yuji’s mother and used that body to give birth to Yuji, making Yuji another product of the same “parent.”
  • During their fight in Shibuya, when Choso is about to kill Yuji, he suddenly experiences “false” memories of them spending time together as siblings, which shocks him and flips his perception of Yuji from enemy to family.
  • After realizing Kenjaku is the same entity as the cruel “Noritoshi Kamo” who created the Death Paintings, Choso concludes that Yuji is also his relative through Kenjaku and starts treating him as his younger brother, fighting alongside him and protecting him.

So, in-universe:

  • Same origin (Kenjaku) → “same parent.”
  • Shared blood/cursed lineage → Choso accepts Yuji as his little brother.

Emotional / Character Reason

  • Choso is extremely attached to his brothers Eso and Kechizu and built his identity around being their protective older sibling.
  • When they are killed, he’s shattered and initially wants revenge on Yuji; once he realizes Yuji is also a “brother,” that instinct to protect flips toward Yuji instead of against him.
  • From then on, he:
    • Calls Yuji his “little brother” constantly.
    • Steps in to save and train him (including helping with blood techniques once Yuji loses Sukuna’s power).

It’s half bloodline logic, half Choso desperately needing to hold onto his role as an older brother.

How Yuji Feels About It

  • At first, Yuji is confused and doesn’t really buy the “we’re brothers” claim; he mostly just rolls with it because Choso is now an ally and they have bigger problems.
  • As he learns more about Kenjaku and his own origins, Yuji starts to lean toward accepting that Choso might truly be his brother, but he still isn’t fully certain.
  • In Japanese, Yuji uses the informal “aniki”-style way of referring to Choso—something that can be used for a mentor/older-brother figure even if you’re not 100% sure about blood relation, reflecting that he accepts the bond at least on an emotional level.

So Yuji’s stance is basically:

“I don’t fully get how , but… just treat him as my older brother.”

Why It’s Such a Big Fandom / Forum Topic

This whole “why does Choso call Yuji brother” thing turned into a fandom meme and a serious lore question at the same time:

  • Lore angle: People debate whether to classify them as “half-brothers via Kenjaku,” “cursed siblings,” or just “spiritually” related.
  • Emotional angle: Fans love how over-the-top sincere Choso’s big-brother energy is, especially contrasted with Yuji’s initial confusion and later soft acceptance.
  • Ongoing discussion: Forum threads and subreddit posts keep revisiting whether Yuji truly accepts Choso as his brother and if he’ll call him that clearly and directly more often on-screen.

Mini FAQ

Is it just a joke or meme in-story?
No. It starts from a real plot point (shared origin via Kenjaku) and becomes a genuine, serious bond for Choso, even if fandom has turned it into a running joke.

Are they “real” brothers?
They’re not traditional siblings born from the same normal parents, but by JJK’s logic—same “parent” (Kenjaku), shared blood/cursed lineage, and mutual recognition—yes, they count as “brothers” in-universe.

Why is Choso so intense about it?
Because his whole identity is built on protecting his younger brothers, and accepting Yuji as a brother gives him a new purpose after losing Eso and Kechizu.

TL;DR: Choso calls Yuji “brother” because they both come from Kenjaku’s experiments, making them relatives in the JJK lore, and Choso wholeheartedly accepts that role as Yuji’s fiercely protective big brother.

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