The year is 2174.
All Might has begun his debut into the world of heroes. The ropes of society are constraining into less fear of villains taking over and slowly shifting towards heroes being the main focus. However, major organizations such as the League of Villains are not yet in total power yet. The same can be said for major villains such as Tomura Shigaraki. However, All for One is still gaining power and trying to build his army.
A man named Abara Totsune is living in Hosu City, working as an expert of quirk sciences for the Japanese government. Though he isn't well known in the public's eyes, he is a stellar inventor that has all sorts of gadgets and top-of-the-line tech at his disposal. He was born quirkless, and therefore he decided to spend all of his time studying the science of quirks; and today, he's made a breakthrough.
He has created a device that gives quirks to the quirkless. However, he realizes that it requires the quirks of others in order to function. So, naturally, he created a device that would inject a needle into a person's body and extract DNA, which could be used in order to create "helixes" that would later become quirks. However, Totsune soon realized two things that would make his breakthrough, though revolutionary, an interesting problem to solve. One: What would happen if a person was given the DNA of two different quirks? Would they become a Noumu? Would they get rid of their old one and gain a new one? Honestly, he had no idea, but on a side note, he discovered a single helix alone wasn't enough to give a quirkless person a quirk.
In order to mitigate these issues, he ran a few more simulations and calculations to iron out the kinks in his theory. He created a device that would allow him to extract DNA from targets at a distance, which he dubbed the Extension Needle. However, there was one unknown variable missing, one thing that would keep him from realizing his dream. So, on he waited. He continued his own physical development as well as his plans for the future, should he be able to use his device to its fullest potential. He was ready to give himself a quirk, when the time would finally come.
26 years later...
The year is 2200.
All Might has just finished off All for One for good with the United States of Smash. His leaving the scene of heroes for good has caused a ripple effect across the world, making villains more prevalent without an overlord watching over them and no one to lead them. In the fight between the two superpowers, All for One was left dead. As the whole world witnessed this event, Totsune did as well. He'd been observing All for One in general, mainly because of his quirk, and the potential it had for his helix development. All for One's corpse would be buried soon, but Totsune had a plan. He was going to steal the head of All for One in order to develop his helixes as well as their devices.
He did so with very minimal effort. Drone tracking wasn't all that hard to do, and no one really cared about a corpse, so not many security measures were put into place to keep its location a secret. On the day of his burial, Totsune observed the event from a drone. He waited until nightfall, and then snuck into the graveyard to dig up his grave. He then pried it open with the tools he had on hand, and quickly headed home. He made sure not to leave any evidence or witnesses that he was there.
Once he had All for One's head, he could begin extracting his quirk; and so he did. As he theorized, it was one of the key components in creating his machine. He discovered that he, using the technology of All for One's Helixes as well as his own advanced tech, could take apart individual properties of quirks and fuse them with other properties from other quirks, in order to genetically engineer quirks to be the most useful for whatever task they were intended to perform. He quickly realized the gigantic scale and implication of this achievement, and decided to name this creation the Quirk Fusion Device.
Once he knew his goal, he set off on a hot pursuit of DNA. He began collecting helixes of all different types, assembling an arsenal of ingredients to create quirks with. Once he completed his quest for helixes, he finished by creating a solution that would solve not only his own problems, but the problems of quirk society itself; And so, a solution was made. Totsune gathered his resources and infected the water supplies of one nation after another. The ripples this had were unprecedented.
Every person now had a quirk, including the previously quirkless. Those without quirks were given a weakened form of One for All, known as Small for All, which allowed them to be given a fighting chance in the world of quirks. This was caused by One for All's spreading gene, which allowed the quirk to be held across multiple individuals. However, since it was no longer concentrated, it lost most of its power and drawbacks, to the point that the quirk could not be used for its previous grandiose attacks, and would be restricted to hammering through walls. Those that had previously had quirks had them mutated, creating a chain effect of new quirks in the world. No one had their previous quirk, and everyone had a new "fusion" quirk. The new generations would also have fusion quirks, and all the while, Totsune would go on to develop his magnum opus, a quirk that could rival the strongest quirks in the world. A quirk to maintain order and keep his new society in balance - Wing for All. And such, the story of My Hero Evolution began.