Bleach is a classic shonen title with a beloved hero, Ichigo Kurosaki. Although Ichigo was born a seemingly ordinary human being, he has ancestry from both Soul Reapers and Quincy, and when he met Rukia Kuchiki, his true powers were awakened at last. He has challenged the strongest foes in the Bleach universe and won.
In some ways, All Might, the symbol of peace, isn't too different from Ichigo Kurosaki. All Might was born Quirkless in the My Hero Academia world, but he had the heart of a hero and obtained new powers which he used to defend the people against evil, at the risk of his own life. If these two heroes were to clash, however, only one would remain standing by the end.
Ichigo Kurosaki: The New Swordmaster
Ichigo Kurosaki didn't take much interest in swords until he obtained one upon awakening his Soul Reaper powers. He used a generic zanpakuto at first, but after training with Kisuke Urahara, he obtained his true sword, Tensa Zangetsu. This mighty sword is quick and sharp, with a fearsome shikai mode. After Ichigo trained some more with Yoruichi Shihoin, he could access his bankai as well. The bankai mode, Tensa Zangetsu, is a long, thin black blade that compresses its spirit energy for maximum speed and cutting power. Ichigo can move with blinding speed when in bankai mode, and nearly defeated Captain Byakuya Kuchiki, an experienced Soul Reaper, with this blade.
Soon, Ichigo realized that he had a hidden power inside: a Vasto Lorde Hollow that hungered for battle and fought on pure instinct. Ichigo had to tame this power by visiting the Visoreds, ex-Soul Reapers who had learned to use Hollow masks in battle. Now, Ichigo has a firm grip on his inner Hollow, and he can boost his speed, power and stamina when he dons a Hollow mask. In extreme emergencies, such as his death, Ichigo will mutate into a Vasto Lorde, a being with enough power to take on the fearsome Ulquiorra Schiffer and finish him.
Ichigo has few ranged attacks and cannot perform kido spells. However, he can charge up his spirit energy and launch it with the Getsuga Tensho technique, an ability that powers up with bankai mode and while Ichigo has his Hollow mask on. In some cases, Ichigo wraps the Getsuga Tensho around his zanpakuto to increase its melee damage.
All Might: The True Symbol
Toshinori Yagi was born without a Quirk, but as an adolescent, his heroic heart impressed Nana Shimura, and she gifted him the One For All Quirk. He underwent extensive training with Gran Torino (like Izuku would later do), then became something of a prodigy. The boy who soon called himself All Might realized his potential with astonishing speed, and as a young man, he was already an international star. In his earlier hero days, he would visit the United States to see his friend David Shield, and he had long since inspired Mr. Shield to realize his own potential and fight villains however he could. All Might even named his California Smash technique in honor of his friend.
All Might's speed, strength, stamina and courage are seemingly boundless, and most villains are blown away with a single punch. Single-handedly, All Might serves as a beacon of courage and hope for the entire world, acting as a one-man dam against villainy, tyranny and fear. If All Might faces a serious foe such as the dreaded All For One, he will use his earth-shuddering Smash attacks and blast his enemies away. These Smashes act as ranged attacks, in a way, since the sheer force can project itself rather far and strike enemies who are beyond the reach of All Might's knuckles. All Might has a sharp tactical mind and is capable of some psychological warfare, using his formidable reputation to demoralize villains. If truly pressed (which is rare), he can go Plus Ultra and break beyond his limits to land the final blow.
The Battle: Zanpakuto Vs Plus Ultra
In this fight, Ichigo and All Might will charge at each other with all they've got, and Ichigo will only narrowly avoid All Might's first blow. Shikai is far from enough; Ichigo will activate bankai to keep up, and now he can avoid the worst of All Might's barrage of fists. Landing a blow in return will be difficult, though; All Might is faster and more agile than he looks, and Ichigo will struggle to slash him with his blade. It'll take a point-blank Getsuga Tensho to survive a retaliatory Smash attack.
Now Ichigo will don his Hollow mask for maximum power, and he can fight All Might more comfortably this way. However, his Getsuga Tensho is a bit too slow to hit All Might, and the symbol of peace can blow it away with a Smash attack anyway. Once All Might has tired Ichigo out, he will go Plus Ultra and deliver a terrific Smash that will blast Ichigo high into the sky and far away. Ichigo won't have a chance to use his inner Hollow; All Might is the winner.