For a time, My Hero Academia's biggest star was the invincible symbol of peace, All Might. During his reign at the top, All Might could keep villainy and crime at bay with his sheer presence and reputation. To this day, no other hero has achieved such a feat. All Might is practically invincible in combat when wielding the full power of the One For All Quirk.
But he's not the only melee powerhouse in anime. The Naruto world has its own champion in Might Guy, who was eventually recognized as a legendary shinobi and one of the Leaf Village's ultimate fighters. Might Guy set a new standard for taijutsu, but is it enough to overcome the power of One For All? Might Guy will give it a shot.
What All Might Can Do
All Might's greatest fans, such as Izuku Midoriya, would say it's much faster to list what he can't do. In his youth, All Might was born Quirkless, which made him an ideal vessel for One For All when its 7th wielder, Nana Shimura, granted it to him. All Might quickly gained the muscular body necessary to contain that Quirk, mastering it even more so than any previous wielder did. He benefited from how much time the previous wielders had spent charging up One For All, and combined with his own incredible physique, this made him an unrivaled melee powerhouse -- both before and after sustaining that grievous injury at the hands of All For One.
Official My Hero Academia stats make it abundantly clear: All Might set a high standard that might never be surpassed. His stats are all 6/5, or S-rank, and his sheer strength with One For All is legendary, allowing him to pulverize any foe into oblivion with just one strike. He can level entire city blocks with that power, or send a villain flying miles away in the sky, never to be seen again. There's a superhuman speed to match, being able to evade enemy attacks and maneuver across the battlefield faster than the eye can see. All Might is also a smart and perceptive fighter, able to deduce the enemy's strengths and weaknesses and exploit them.
This is further augmented by All Might's incredible will: regardless of the danger, he never backs down from a challenge in My Hero Academia, and having people to save pushes him beyond his limits if he must go Plus Ultra. Even when all seems lost, such as when he fought a specialized Nomu or his archenemy, All For One, All Might had the will to prevail, and he can deliver a United States of Smash to finish the job.
What Might Guy Can Do
There's a good reason why this Leaf Village ninja also has "Might" in his name. He is practically the All Might of the Naruto universe, an unrivaled taijutsu master with nerves of steel and a heart of gold. Might Guy is capable of ninjutsu, but taijutsu is where he shines brightest.
He has spent a lifetime honing his body with rigorous exercises and boundless enthusiasm to match, never wavering in his belief that he can become the best through hard work (an example that characters such as Rock Lee and Naruto Uzumaki would follow). It paid off, and Might Guy became a taijutsu terror on the battlefield. Even the likes of Itachi Uchiha respect his power, and Might Guy's ability to open the eight Gates and use special techniques can rival any kekkei genkai.
Might Guy's default power is astonishing, but he can also open one Gate after another to use techniques such as Front Lotus, Reverse Lotus, Morning Peacock and Daytime Tiger, which also create unique visual effects as they are executed. Abilities like these can challenge even a tailed beast, including the Ten-Tails, and Might Guy came impressively close to defeating the seemingly unstoppable Madara Uchiha with nothing but taijutsu and nunchucks on his side.
The Showdown: All Might Vs Might Guy
Both heroes will agree to a polite but no-holds-barred melee showdown, and they will begin in a wide, open arena just outside the Hidden Leaf Village, where no one can get in the way. All Might has the advantage with his slightly superior power and technique, but Might Guy can survive the worst of his attacks, then access the Gates to take things to the next level. Regular taijutsu won't cut it.
Naruto's Might Guy will open the first Gate, then the third, and push All Might back with his Lotus techniques. Now All Might must respond with a Texas Smash to keep up, and it's working. Might Guy is taking damage, and he'll need the sixth Gate and the Morning Peacock technique to stay in the fight. All Might can neutralize this with a heavy-duty Smash, however, and before Might Guy can open any more Gates, My Hero Academia's symbol of peace will show off his ultimate move, the United States of Smash, and honorably end this battle before things get really messy. All Might has won.