Rachel Bloom has an exciting new addition to her songwriting credits. She's creating music for an upcoming The Flash-Supergirl crossover episode, and she has the perfect cast to do it justice. Grant Gustin and Melissa Benoist will sing "Super Friend" on the shows' second crossover episode. Darren Criss, who co-starred with both actors in Glee, will guest-star in the musical. Our fingers are crossed that he'll also find his way into the song somehow. The combination of Supergirl and The Flash appealed to Bloom so much that she approached The CW's president, who put her in touch with executive producers Greg Berlanti and Andrew Kreisberg. Once she came up with an idea they liked, she and Robot Chicken's Tom Root got to work on the song. "I am so excited to contribute more to the upward trend that is musicals in television and film. Music can be one of the most amazing and efficient forms of storytelling and character development," she said in a statement to BuzzFeed. "Also, it was really fun to write a comedy song for two superheroes." The episode will air March 21 on CW, following the Supergirl crossover episode on March 20.