It's time for The CW's Supergirl to form a dynamic duo of its own. The Arrowverse series -- which is midway through its third season -- has largely kept the show's cast of characters within the family, focusing on Superman staples like Jimmy Olsen, Cat Grant, General Sam Lane and the big blue Boy Scout himself. Now that the show has established its cast and tone, though, it may be time for Supergirl to branch out to include other characters from DC's expansive canon -- and we know someone who would be a perfect fit: Batgirl.
Over the past three seasons, Supergirl has established Batman and his crime-ridden city of Gotham as part of her universe. In Season 2, Kara offhandedly mentioned that her cousin Superman worked with a "crazy" vigilante with a lot of gadgets. The show has also namedropped Gotham on several occasions. What's more, Batman exists across the Arrowverse's established multiverse; in the first season of DC's Legends of Tomorrow, Rip Hunter mentioned “Dark Knights” in the first season of the show, clearly referencing Batman. As such, the series has laid the groundwork for parts of Batman's world to bleed into Supergirl, even if the Dark Knight himself doesn't show up. Plus, if Supergirl can make it a whole season without Superman, Batgirl is more than capable of managing without Batman.
Additionally, Batgirl and Supergirl have a lengthy history of teaming up with one another. They got a whole crossover episode to themselves in the Batman: The Animated Series episode "Girls' Night Out." In Super Best Friends Forever, a series of animated shorts by Cartoon Network, the two were joined by Wonder Girl for a brief series of madcap adventures. Most recently, Batgirl and Supergirl joined forces in 2017's Batgirl Annual #1 for a case that continued into Supergirl's solo series. DC Comics even has a whole page -- including some additional comic recommendations -- dedicated to their friendship on its blog.