Marvel Comics' Free Comic Book Day special will set up an X-Men / Avengers crossover. The relationship between the X-Men and the Avengers has always been a tense one. Few Avengers have been there for the mutant race in their times of need - the Avengers didn't even react to the mutant genocide on Genosha, when 16.5 million mutants were slaughtered by rogue Sentinels. The X-Men have never forgiven this, with relations between former lovers Emma Frost and Tony Stark breaking down. Matters came to a head in 2012's "Avengers Vs. X-Men" event, when the two superhero teams collided over the fate of the mutant race. The Phoenix Force had come to Earth; the Avengers believed it threatened to destroy the entire planet, while the X-Men hoped it would reignite the mutant gene and prevent their race from going extinct.
The modern X-Men and Avengers now operate on a greater scale than ever before. The Avengers are now led by Black Panther, and they're based in the body of a giant Celestial; they possess power on a cosmic scale, including one member who is - ironically - the new Phoenix Host. Meanwhile, the X-Men have established a mutant nation on the living island of Krakoa, where the mutants have learned to synergize their powers to spectacular effect - even conquering death itself. But there have long been hints the two superhero groups will wind up against each other once more, with the X-Men objecting to Wakanda's refusal to trade with Krakoa.
Now, Marvel Comics has announced they will celebrate Free Comic Book Day 2021 with three exclusive issues, including Free Comic Book Day: Avengers/X-Men #1. This will feature stories by Kieron Gillen, Gerry Duggan, Dustin Weaver, and Matteo Lolli, and according to Marvel it will "lay the groundwork for an event that will take the Marvel Universe by storm in 2022 and forever change the relationship between Earth's Mightiest Heroes and mutantkind."
It's likely the Phoenix Force will once again lie at the center of this. A recent teaser for the upcoming Immortal X-Men series suggested there's still a vacancy on Krakoa's ruling Quiet Council - and the vacant throne bore the insignia of the Phoenix. Significantly, this book is written by Kieron Gillen, which supports the theory there's a connection between the Free Comic Book Day one-shot and her Immortal X-Men series. Jason Aaron's Avengers run has redefined the Phoenix, even revealing a Phoenix host is the true mother of Thor Odinson, so hopefully this event will explore the impact of this revelation.
For decades now Avengers and X-Men crossovers have been a mainstay of Marvel Comics, and they've told some of Marvel's biggest stories. But the potential is there for this to be one of the biggest to date, simply because the two teams have status quos that are a radical departure from their traditional portrayals. The Free Comic Book Day: Avengers/X-Men one-shot should be unmissable.