The big twist in James Gunn's Superman has been contentious among fans, with many still coping with the idea that Jor-El's message to his infant son was somehow tampered with. However, Gunn quickly confirmed that the message from Bradley Cooper's Jor-El was genuine, even questioning how audiences could "not think it's real?" despite the film's exposition affirming its validity through Nicholas Hoult's Lex Luthor and even Edi Gathegi's Mr. Terrific. But many fans have begun to try poking holes into this plot point through Superman's cousin, Milly Alcock's Supergirl.
After all, David Corenswet's Superman knows his cousin well enough that he casually babysits her ill-behaved dog, Krypto, while she parties on planets with red suns to get drunk. Clark could have asked Kara about his father's message and whether his thoughts reflected those of Krypton.
In an extensive interview, Rolling Stone even asked James Gunn why Superman didn't do just that, considering Supergirl should be "more knowledgeable about Krypton" than her cousin.
Gunn denied that Supergirl could have helped, clearing up that while not "everybody on Krypton is the same," like Jor-El, "[Kara] wouldn't know anything about [Superman's] parents" since "she's younger than him:"
"You're assuming that everybody on Krypton is the same! And how would she know? She's younger than him, so she wouldn't know. She wouldn't know anything about his parents."
Side-stepping why Kara couldn't or didn't tell Superman that not all Kryptonians were like his father, Gunn's mention of her being younger than Superman has fans concerned.
It's possible that Gunn misspoke or wasn't clear in explaining his reasoning on why Kara couldn't help, but his words strongly suggest that she would be unaware of Jor-El's true nature and why he sent his son to Earth because she would have been too young to know him—if she were born to know her uncle at all.
How This Change Could Mess up Supergirl's Tragic Origin
What has fans worried about Gunn's answer is that Supergirl in the DCU could be using her Pre-Crisis origin, in which she was born on Argo City after Krypton's destruction, instead of her Post-Crisis origin, where she lived on Krypton as a teenager until the planet's annihilation, surviving on a bubbled Argo City floating through space. Both origins end with her being sent to Earth, but have dramatically different effects on the character.
Additionally, while she arrived on Earth at half of Kal-El's age in the Pre-Crisis origin, she and her ship were frozen in stasis in her Post-Crisis origin. This stasis halted her aging and made Kara chronologically older than her cousin, but biologically younger, adding an extra layer of frustration for the character lost in her Pre-Crisis origin.
What's extra confusing about Gunn's wording is that Tom King's comic book Supergirl: Woman of Tomorrow, which her upcoming film is heavily based on, uses the Post-Crisis origin as a means of making her relationship to Krypton extra tragic, as she was 13 years old before the planet's destruction. Kara would subsequently live another year on the floating, shielded city of Argo as it and its people would slowly die of Kryptonite poisoning before being sent away by her dying father to Earth.
On top of that, in some continuities like New 52, Kara Zor-El explicitly knew and spoke with Superman's parents, even holding her baby cousin on more than one occasion, directly contradicting Gunn. That is, unless the DCU's Supergirl has her Pre-Crisis origin instead, never being born to meet her now-dead relatives.
One explanation that could account for Kara's Post-Crisis origin and her not knowing her father's brother is that her parents forbade Kara from seeing them due to Jor-El's unconventional beliefs that did not align with Krypton. Similar to how Jor-El in the New 52 continuity became distant from Kara's father for his questionable experiments.
A mess for an origin, and still not explaining why Kara couldn't tell Superman that, no, not everyone on Krypton was a weird eugenicist like Jor-El, but it would at least preserve Supergirl's more tragic origin. Regardless, writer Ana Nogueira has been given the arduous task of rehabilitating Krypton's image in the eyes of the general audience with Supergirl, after Jor-El and his message framed them as conquerors.
After all, Kara is a drunken mess in Gunn's Superman for a reason: Unlike her cousin, she misses Krypton.
