Beimax has a big red fist glove that shoots out of his hand, Doomfist's Gauntlet looks exactly the same and probably shoots out just the same.
Only explanation is that Doomfist is Beimax... in the future after beimax gets trapped in that portal thing when he 'dies' at the end of the movie.
Really the portal is the Overwatch universe, where he ends up developing his red armor into blue and becoming a straight badass because he gives the tadachi chip to Hiro.
As we saw when beimax fought the micro bot guy without the tadachi chip went berzerk af and his eyes turned red.
Since Hiro has the tadachi chip Beimax is probably going insane in that portal and naturally developed into some evil being, who i would proclaim is called "doomfist" and yeah.... k bye