Casey's dad, Jeff Pearlman, tweeted a photo of the superhero duo on Saturday, saying, "My daughter is Jewish. Her best pal is Muslim. For Halloween they created a superhero team: The Juslims. I've rarely been more proud. Truly."
The tweet has since gone viral, with tens of thousands of people sharing it.
Pearlman, a best-selling author with 50,000 followers, told BuzzFeed News that he's never had a tweet go this viral.
"There's just so much hostility in the air and in this election season," Pearlman said. "This was just a refreshing, innocent reminder that we don't have to be this way. We do not have to let this divisiveness take over right now."