WARNING: The following contains major spoilers for My Hero Academia: World Heroes' Mission, now screening in theaters.
The climax of My Hero Academia: World Heroes’ Mission sees Deku finish off the main villain with a new ultimate move: the United States of World Smash, a name clearly inspired by All Might’s United States of Smash. The scene is spectacular, but it begs the question of how far along Deku is in mastering One For All. The fact that he can pull off such a powerful move suggests he’s getting close to his goal of using 100% of OFA’s power.
That said, comparing the two finishing moves is not as simple as it sounds. The names may sound alike, but that’s where the similarities end. That doesn’t mean United States of World Smash can’t be used to track Deku’s progress, however. Let's take a look at both his and All Might's signature moves.
Firstly, it’s important to note the key differences between All Might's United States of Smash and Deku's United States of World Smash. For starters, United States of Smash is a singular punch that calls upon all the user’s available strength. United States of World Smash is more of a combination attack that involves dealing multiple powerful blows to the target before finishing off with a powerful kick. The similar name structure indicates that Deku's World Smash, like its inspiration, requires all the user’s strength in order to be utilized properly.
There is also a notable difference in both moves' power output. When All Might uses United States of Smash in My Hero Academia, it creates a massive crater and a tornado powerful enough to lift buildings off the ground. Deku's United States of World Smash, while powerful, doesn’t do nearly as much damage to his surroundings in World Heroes' Mission. This could simply be because the villain he uses it on, Flect Turn, absorbs most of the impact with his Reflect Quirk. The more likely explanation, however, is that United States of World Smash, despite its cooler name, is not yet on the same level as All Might's signature move.
It’s not unlike Deku to give his moves better-sounding names than what they actually are. In his battle against Muscular, he finishes the villain off using a Delaware Detroit Smash with 1,000,000% of One For All’s power -- or so he says. According to MHA creator Kohei Horikoshi, this is closer to a battle cry than a statement of fact. If Deku were actually somehow able to use 1,000,000% of One For All’s power, the damage would be far greater than simply knocking out a villain and breaking a few bones.
Deku’s variation on United States of Smash is likely a result of his lack of mastery of One For All. Since he is still unable to use One For All at 100% without injuring himself, he must be relying on multiple smaller attacks so he doesn't have to put as much power into the finishing blow. This would also mean that even if he is going past 100% to pull off the final attack, it’s still not as far past 100% as All Might goes for his singular, use-everything-at-once attack.
It’s also worth noting that in World Heroes' Mission, Deku’s injuries aren’t nearly as severe after using United States of World Smash. At the end of the movie, Deku returns to America with relatively minor injuries as far as broken bones go. This could mean one of two things: either Deku isn’t using One For All at 100% to use United States of World Smash, or he is using 100% or more but is finally at a level where it doesn’t hurt him as badly. The more likely answer is the latter, which would indicate that Deku has made great strides in mastering One For All.
World Heroes' Mission makes it readily apparent that Deku is getting more and more comfortable with his use of One For All. He has to alter how he uses it in order to minimize the wear and tear on his body, but that’s been the norm since he started using Shoot Style. His ability to leave a fight with fewer broken bones also shows how much more durable he’s become as My Hero Academia progresses. Deku may still be a long way from mastering One For All, but if United States of World Smash is any indication of his progress, he’s definitely coming along well.