Supergirl executive producer Andrew Kreisberg told Entertainment Weekly that not only will audiences see more of Kara and Alex together in the "Midvale" episode of Supergirl's third season, but that the four-episode crossover event will also be very Danvers-centric.
"Kara and Alex are at the center of it through all four hours. One of the things we've been doing a lot this season is getting back to season one and really making it Danvers sisters-centric, so a lot of what's going on this season is Kara and Alex doing things in tandem, and the crossover won't be any different," Kreisberg said.
News of a Supergirl-centered crossover will be welcome news to fans who felt like the Girl of Steel was shortchanged in last season's crossover event. Last season's crossover was kicked off in a very brief scene at the end of episode eight of Supergirl that felt more like an afterthought than a real part of the event. Fans didn't feel like Supergirl was incorporated or utilized enough in the overall crossover either, as none of her supporting cast got to come along for the adventure. However, with Alex's participation being confirmed this season, it strongly suggests that the crossover will take place on Supergirl's turf, Earth-38.
The crossover being on Earth-38, and possibly even directly in National City, would also mean that we would see Supergirl supporting characters, such as Jimmy Olsen and Martian Manhunter, taking part of the action while various supporting Arrow and Flash characters could remain off screen presenting episode opportunities of its own. Supergirl, if you remember, barely appeared in one episode of her own show last season because they used the time that she was participating in the crossover to make a supporting character-centric episode that tied up various plot threads. If this upcoming crossover does take place on Earth-38, it could open the door for Arrow to do much the same, including exploring Black Siren's backstory at a time when the character might be deciding if what side she truly wants to be on.
Supergirl will premiere on October 9th. The Arrowverse crossover event will take place on November 27th and 28th.