My Hero Academia's combat system is centered around supernatural Quirks. It's a world of heroes, but if those heroes are corrupt or go rogue, then the hero killer known as Stain will intervene and assassinate them in cold blood. His skills and Quirk are perfect for dispatching lone victims in a dark alley.
Meanwhile, in Avatar: The Last Airbender, the Avatar the unique individual who can bend the four classic Greek elements and summon the Avatar state to maintain peace and balance in the land. If there's ever an inter-universe crossover and Stain decides that Avatar Aang is a problematic hero, could he succeed in assassinating the Avatar?
Stain's Powers & Abilities
Stain the Hero Killer is a dedicated assassin, though he doesn't sell himself out as a hitman. Instead of performing contract killings, Stain decides on his own which superheroes are truly worthy of the cape, and which are hopelessly corrupt. Stain is more a vigilante than a true villain, but he's a serious threat all the same.
Stain has remarkable physical abilities, boasting extreme speed, incredible agility and sharp reflexes. His physical strength is impressive, but his real asset is his ability to track down a target within an urban environment and ambush them with blinding speed. Stain is not the type to seek out honorable duels; instead, he stalks unworthy heroes and takes them by surprise in cramped confines, such as back alleys. Stain has also been seen sitting atop skyscrapers in broad daylight, so he can scope out the entire city.
Stain's equipment includes a jagged katana and a variety of knives and throwing stars, all for the purpose of cutting his opponents and obtaining a blood sample. Stain isn't trying to slice and dice his foes; he just needs to ingest a blood sample to activate his Quirk, named Bloodcurdle. Once it activates, Bloodcurdle will paralyze the target for a few moments, with the exact duration being based on the victim's blood type. This buys Stain more than enough time to deal the finishing blow. In practice, Stain can use his stealth, blades and Quirks to injure and paralyze his target before they can even bring their own Quirk or combat skills to bear.
Avatar Aang's Powers & Abilities
Aang, the reincarnation of the Fire Nation Avatar Roku, was born in the Air Nation before the Hundred Year War. Aang was always a gifted and creative Airbender, but at age 12, he learned about his true nature, and the Airbender monks prepared for Aang to learn the other three elements. Aang couldn't handle the responsibility and ran away as the war broke out, freezing himself in an iceberg for the next century.
Despite his goofy disposition, Aang is a smart, tough and courageous bender who grows into his responsibilities of keeping the peace. Aang is a quick and resourceful thinker, like most Airbenders, and he has the benefit of bending all four elements at once. Aang was a natural Waterbender when Katara and master Pakku trained him, learned to bend his opposite element Earth from Toph Beifong and finally mastered fire alongside Prince Zuko. Aang can easily switch from one element to another in battle, and this means he has very few (if any) blind spots. He can leap about on jets of air, freeze his enemies with water, create barriers with earth and finish off his foe with blasts of flame.
Aang can also enter the Avatar State, either by will or during moments of distress. The Avatar state gives Aang access to the memories and abilities of all previous avatars, from Roku and Kyoshi all the way back to Wan. In this state, had the power to turn the tables on Fire Lord Ozai, trap him with earth and defeat him with the unique art of energybending, taking away the Fire Lord's own bending abilities.
Stain Vs. Aang - Who Would Win?
There are two ways the duel could start: either Stain ambushes Aang in an urban environment and lands the first blow, or Aang confronts him directly. If Stain can begin the fight on his own terms, he will certainly land the first blow, obtain that much-needed blood sample and render Aang paralyzed. This could be his chance to finish Aang off... but he wouldn't be given that chance.
Aang would now aware of the danger, and the Avatar State would take over. The sheer power of Raava and the Avatar State could move Aang's body despite his injuries, and this sheer power would blow Stain away and protect Aang from any further harm. And if Aang fights Stain fairly from the start, his bending can block Stain's abilities and force him to retreat. The Hero Killer simply can't take down the Avatar.