Supergirl will make her onscreen DCEU debut in The Flash, but the movie could waste a fascinating detail of her origin, depending on which iteration of the character it uses. The Flash will loosely adapt the 2011 crossover story Flashpoint, which involves time travel, alternate universes, and an ultimate continuity reboot for DC Comics. The Supergirl played by Sasha Calle might be Kal-El’s cousin, Kara Zor-El, or another character from the DCEU multiverse, but the former would allow for interesting characterization opportunities which would further differentiate Supergirl from Superman.
Zack Snyder's Man of Steel first showcased the DCEU’s iteration of Krypton and Kryptonian society. For generations, Kryptonian progress seems to have halted, with the species destroying the planet Krypton’s environment and genetically engineering its populace for specific societal roles. Kal-El, the eventual Superman, was Krypton’s first natural birth in centuries, giving him something that no other Kryptonian had at the time: Free will. Thanks to his refugee status and having the Kryptonian Growth Codex bonded with his cells, Kal-El carried the future of his people within him, in both a figurative and literal sense.
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Little is known about Sasha Calle’s iteration of Supergirl in The Flash, but it is speculated that she will be an alternate universe version of Kal-El or perhaps the child of Clark Kent and Lois Lane from the future. If Calle ends up playing the main DCEU timeline’s version of Kara Zor-El, however, she has fascinating potential as a protagonist since she’d be older than Clark Kent and, therefore, part of Krypton’s outdated system of genetic
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