From the moment Mahershala Ali was confirmed as Blade at San Diego Comic-Con in 2019, speculation mounted about where his first appearance could come. It was thought Marvel could save his introduction for the Blade solo movie, but the MCU also has a habit of featuring future leading heroes in other properties first. This led to theories that Mahershala Ali could appear in various Phase 4 projects ranging from Doctor Strange in the Multiverse of Madness to Moon Knight. While both of those could still happen, neither of them proved to be the right place to bring Blade to the MCU.

Related: How Eternals' Credits Scene Sets Up Blade's MCU Future

At first glance, the decision to put Blade's MCU debut in Eternals seems incredibly unexpected. Blade and the Eternals have a low level of crossover in the comics, which is why most weren't anticipating the vampire to have any involvement. From what has been said about Blade's Eternals debut by those involved, it came down to the decision to use the Ebony Blade in the post-credits. While Eric Brooks is a skilled swordsman, it has been said that Dane's new sword has similar characteristics as vampirism. The exact nature of the link between Blade, Black Knight, and the Ebony Blade is unknown currently, but Marvel's decision to potentially change the weapon's powers or origins could explain why Mahershala Ali debuted in Eternals, despite other viable options.

As a result of Blade's MCU debut coming in Eternals, there are plenty of possibilities for what Marvel could reveal about him and the Ebony Blade. It is possible Blade once possessed the famed sword, possibly before Dane's uncle, and that bond brought a vampiric connection. Some speculation also suggests that the Ebony Blade could be tied to the origins of vampires in the MCU. The Ebony Blade has a blood lust and curse in the comics, so these elements could've been reconfigured to align with the blood-sucking beings. There is also the chance that this was all done to lay the foundation for Blade and Black Knight to be MI-13 teammates.

Blade's Eternals appearance may have been a surprising place for his MCU debut, but it is possible the decision was partially dictated by the MCU slate. It is expected that Blade will release in theaters sometime in 2023, and the vampire hunter isn't an easy character to fit into any project. Marvel may have determined that Eternals was the best place to tease audiences with Mahershala Ali's Blade. It was also a fairly easy debut to pull off since it didn't require the actor to film anything.

More: Everything We Know So Far About MCU Blade