As the release date for My Hero Academia: World Heroes' Mission draws near, speculation has begun regarding whether the series' latest film will be canon. Traditionally, films exist outside of their anime's official canon, as they are usually original stories rather than based on existing material. However, since the success of Demon Slayer: Kimetsu no Yaiba: Mugen Train, the idea of more canon films has been gaining steam, leaving fans to wonder if MHA will follow suit.
The premise of World Heroes' Mission is that a new group of villains called Humarize claim to be fighting for the salvation of the world. They reference the Quirk Singularity Doomsday Theory, which claims future generations of Quirks will become too powerful to control, resulting in the downfall of society. Using a mysterious drug, they are forcing people in densely populated areas to lose control of their Quirks, causing destruction and mayhem that proves their point about the danger uncontrollable Quirks pose to humanity.
Interestingly, the Doomsday Theory idea was introduced in the anime, meaning the argument can be made for the film's existence inside MHA's continuity. It's important to note that World Heroes' Mission is an entirely original story and is not based on existing material. Kohei Horikoshi, the creator of My Hero Academia, is overseeing this new film, meaning he has the leeway to bring elements from the series into WHM.
However, one idea crossing over from anime to film isn't enough evidence. Season 5, Episode 16 of My Hero Academia -- also not based on the manga -- does a great deal to set up World Heroes' Mission, and greatly supports the argument that the film will be canon. Ryuku and Selkie, along with Ochaco and Tsuyu, intercept drug smugglers who possess an unknown, illegal substance that appears to exacerbate someone's Quirk to a dangerous degree, similar to the methods seen used by the Humarizers in the World Heroes' Mission trailer.
That same episode goes a step further with a post-credits scene that indisputably confirms the events of World Heroes' Mission will indeed take place inside the official canon. In this scene, the audience sees the man who appears to be the film's primary antagonist, and he references the fact that the heroes have just thwarted his attempt to obtain more of the illicit drug. He is even standing inside the very same room where the Humarizers are seen meeting in the trailer.
The evidence overwhelmingly points to the idea that My Hero Academia: World Heroes' Mission will indeed be canon. However, considering it is not based on existing material, it remains unlikely that it will have a significant, if any, impact on MHA's plot moving forward. This is not to say the film will be bad -- if it's anything like its predecessors, it will be amazing. Unfortunately, even though it seems highly likely it will be canon, World Heroes' Mission appears poised to be little more than a side quest of minor significance to My Hero Academia's primary story.