Although Supergirl hasn't been established as part of The CW's DC Comics shared television universe - which includes Arrow, The Flash, and the recently premiered Legends of Tomorrow - questions of a crossover began to be raised almost immediately after the CBS superhero drama was announced. With Greg Berlanti acting as executive producer and co-creator on Supergirl, and since he was instrumental to constructing The CW's DC universe, it seemed to be only a matter of time before Supergirl would crossover with The Flash, Arrow, and/or Legends of Tomorrow - though Supergirl executive producer Ali Adler said it was important that the show stand on its own first and foremost.
More recently, talk of crossovers came up again at the Television Critics Association 2016 Winter Press Tour, with Berlanti and CW boss Mark Pedowitz talking about being open to a crossover, then CBS president Glenn Geller further teasing the possibility. Now, we have official confirmation that Central City's CSI tech Barry Allen a.k.a. The Flash (Grant Gustin) will be paying a visit to Cat Grant's assistant Kara Danvers a.k.a. Supergirl (Melissa Benoist) in the upcoming March 28th episode of Supergirl, titled 'Worlds Finest'.
Aside from the date and episode title, though, little is known about the episode at this point, including how the show will explain The Flash's existence in National City - whether The Flash and Supergirl always existed in the same world, or if Barry travels to a different Earth by way of the Multiverse. But, while this crossover may be a good time to establish how Supergirl connects to The CW's DC Comics universe, it could also be the perfect opportunity to give the fans something else they want: a musical episode. So, here's why a Supergirl and The Flash crossover musical could work.
The cast certainly has the chops; both Gustin and Benoist appeared on Fox's musical dramedy series, Glee. Plus, fellow Supergirl cast members Jeremy Jordan, who plays Kara's co-worker Winn Schott, and Laura Benanti, who portrays the identical twin sisters Kara's mother and aunt Astra, are accomplished stage performers. Jordan starred in The Last Five Years, joined the NBC musical series Smash in its second season, and appeared on broadway in musicals like Newsies, Bonnie & Clyde, and Rock of Ages. Benanti, for her part, is a Tony-award winning actress for her role in the 2008 revival of Gypsy, and she has additionally appeared in ABC's country music series Nashville (as well as NBC's The Sound of Music Live!).
Because of all the musical talent at the heart of Supergirl, whether audiences would see the stars put those sets of abilities to use on the CBS superhero drama became a popular question for the cast prior to the show's premiere and in its early months. Jordan, for instance, told Zap2it that his goal in landing the role on Supergirl was to play a part that didn't depend on his musical talents. Although, he also said he "wouldn't be opposed to [singing] if they asked me, but I'm certainly not expecting anything like that. And I'm not pushing for it, either."
Additionally, during an interview with ComicBook.com in which he also spoke about Winn's role as Kara's "fanboy" early in Supergirl season 1, Jordan was asked about the potential of a musical episode:
"You know, that's up to the producers. I think if that happens, wait a second, let us establish these new characters, because people see especially Melissa and I as singers, ahead of being just an actor. I think it would be cool to do that down the line, though."
Benanti also commented to The Wrap soon after the show premiered on the possibility of Supergirl's musically apt cast members contributing to a musical episode:
"We’ve been joking about it. Maybe we’ll do an online one! We’ve been talking about it. Melissa is pretty busy right now. She’s got a lot on her plate, but if she gets some downtime, that’s definitely something we’ve been talking about."
So, when Supergirl first premiered it seemed like a long shot that the writers and producers would be doing a musical episode in the show's first season, but it was something that was on the cast members' minds - whether because they were asked about it so much or because it came up naturally between the musically inclined cast mates. However, now that Gustin has been added to the mix for the March crossover, the call for a musical episode - or, at the very least, a musical component to the episode - has seen a resurgence, prompting an article on The Daily Dot, and generated talk among fans on Twitter.
The Flash already gave fans a nod to its star's musical talent in the season 1 episode 'Crazy For You', and officially established that Barry Allen can perform "Summer Nights" flawlessly at karaoke. Additionally, Supergirl has established that its younger characters - Kara, Winn, James Olsen (Mechad Brooks), and Lucy Lane (Jenna Dewan-Tatum) - partake in a regular game night. So, when the story makes sense, both shows have portrayed its lead characters having fun doing everyday activities of non-superhuman twenty-somethings, which can include singing and/or dancing.
Additionally, Supergirl and The Flash share a much lighter, and at times sillier, tone than fellow DC Comics television shows Arrow (as well as what we've seen so far of Legends of Tomorrow). These tones are established by the shows' shared creative teams that include Berlanti and Flash showrunner Andrew Kreisberg, while series' leads, Benoist and Gustin, carry the lighter tone off exceptionally well - perhaps due to their past work on Glee, which also featured a balance of sometimes-serious, sometimes-silly story content.