Every Marvel Cinematic Universe film features a logo for Marvel Studios at the beginning celebrating the franchise's comic book history using panels taken from various comics, which sometimes change depending on the movie they're appearing before. However, one consistent image is a panel of two heroes kissing.
Their identities were the subject of recent a Quora question. And although Marvel Studios only recently gained the rights previously held by 21st Century Fox, that post revealed the two kissing characters are actually mutants: Justice and Firestar.
Justice and Firestar
Firestar and Justice are New Warriors, which was a fairly popular series in the 1990s. The image in question was drawn by Darick Robertson. Both of them are mutants, whose powers both stemmed from early trauma. Justice/Vance Astrovik was visited by his alternate future counterpart Vance Astro, with the event triggering his X-Gene and activating his telekinetic powers. This caused his father to begin abusing the boy, who ran away from home and eventually joined the New Warriors.
In the comics, Firestar, who had first appeared as a Human Torch stand-in on Spider-Man and his Amazing Friends, was trained by the manipulative Emma Frost after her microwave heat mutation developed. After resigning from Frost’s Massachusetts Academy, she joined the New Warriors, where she and Justice developed a relationship. Their love would face several ups and downs, from the Ben Reilly version of Spider-Man’s flirtation with Firestar to Justice serving a prison term for accidentally killing his abusive father. The two would eventually become engaged and leave the New Warriors for a normal life.
Mutants in the MCU
Given that the very concept of Marvel’s mutants was owned by Fox, who Disney only recently acquired, Marvel Studios was unable to refer to mutants or use X-Men and mutant-related characters. This meant that Quicksilver’s appearance in Avengers: Age of Ultron altered his history considerably, severing his ties to Magneto or the X-Gene.
With Marvel Studios now having the rights to use mutants, Firestar and Justice could theoretically appear at some point in the future. There was also an unaired pilot for a New Warriors TV show, so it may be possible the team eventually appears alongside their classic counterparts and bring another classic panel from the Marvel Studios logo to life.