The following post contains spoilers from chapter 270 of My Hero Academia. You have been warned.
I just got the English version of the latest chapter of My Hero Academia and I now have a better idea of what happened. It looks like Doctor Ujiko did in fact give Tomura Shigaraki the power of All For One, but there is more to it than that. The version of All For One Shigaraki received was not just any version of it. It is the original version of All For One! That means that the All For One quirk we saw All For One use against All Might was just a duplicate while his original quirk was entrusted to Ujiko to give to Shigaraki when the time was right.
However, is there more to this than we think? Did Shigaraki receive the original All For One quirk by itself in its basic form without any additional powers? Did Ujiko combine the original All For One quirk with Shigaraki’s Decay quirk? Did Shigaraki get the All For One quirk along with all the strongest quirks All For One accumulated throughout his career?
Personally, I think Shigaraki gained the original All For One quirk along with the strongest quirks All For One accumulated. This was hinted when All For One revealed himself after stealing Ragdoll’s clairvoyance. He stated that he didn’t need to steal Best Jeanist’s quirk because it did not match Shigaraki’s disposition. This could mean that after All Might weakened All For One, All For One spent the next five years hunting down the best and strongest quirks to give Shigaraki when the time was right. That would include Ragdoll’s clairvoyance.
If it is true that Shigaraki is going to receive all the strongest powers All For One accumulated, does this mean he will still have the ability to steal more quirks? Would Shigaraki become so powerful that he does not even need more power?
Another thing to note from this chapter is that Doctor Ujiko was the scholar who came up with the Quirk Singularity theory. The Quirk Singularity is the belief that as time goes by, the quirks of others would constantly mix with each other one generation after another. Eventually, quirks would become too powerful for anyone to control and it would cause the destruction of both society and the future as a whole. All the experiments Ujiko had been doing from the Nomu to Shigaraki have been leading to an attempt to create the Quirk Singularity.
The Quirk Singularity theory also seems to apply to Izuku Midoriya as well because of the unique nature of One For All. With each generation that passes, One For All has been stockpiling power and fusing with the quirks of its users. When Izuku communes with his predecessors, they claim that they have crossed the “singularity”, which is a clear hint that One For All is somehow connected to the Quirk Singularity theory. This further highlights that Izuku and Shigaraki are foils of one another. Izuku would reach the Quirk Singularity through natural means while Shigaraki would reach the Quirk Singularity through artificial means.
Based on these facts, it is possible that the final battle in the story will involve both Izuku Midoriya and Tomura Shigaraki each becoming a living quirk singularity. If that happens, it will involve both of them reaching their full potential. It will be like two gods clashing with each other as the world around them crumbles away. I look forward to where the story will take.