This article contains spoilers for "Spider-Man: Brand New Day." If you haven't heard already, "Spider-Man: Brand New Day" made hundreds of internet fan theories come true by revealing that Sadie Sink's character is Jean Grey of the X-Men. Even though "Brand New Day" never employs the word "mutant," it's clear that enough have popped up that the government is starting to notice them. Jean is also all alone at the movie's end, leaving her in need of the mentorship Charles Xavier can offer. The way that "Brand New Day" makes "X-Men" set-up a vital part of the story, and gives Jean a complete character arc, echoes one of the most successful backdoor "MCU" pilots: T'Challa/Black Panther (Chadwick Boseman) in "Captain America: Civil War."