WARNING: The following contains spoilers for My Hero Academia, Season 5, Episode 12, "The New Power and All For One," now streaming on Crunchyroll, Funimation and Hulu.
My Hero Academia's joint training arc is complete, and these five battles had more than a few surprises. Not only is Class 1-B catching up to Class 1-A, but Hitoshi Shinso's team pushed Izuku hard enough to awaken a new side of the mighty One For All. Izuku can barely even comprehend this new power, let alone master it.
For now, he is determined to avoid using the strange Blackwhip Quirk until he can better understand One For All, and even All Might and Katsuki Bakugo are concerned about what this means for Izuku's training as a hero. The whole thing eerily reminds them of One For All's original creator, the villain All For One.
In Episode 12 of Season 5, Izuku, Bakugo and All Might meet in secret to hash out what they've seen. All Might mentions that neither he nor his predecessor, Nana Shimura, could access the Quirks of One For All's previous users. It's clear this is a first for One For All, and that may not be a coincidence. The previous wielders stated the time is now, but not even All Might is certain what that means. Is it because Izuku has hit a plateau in his training, or because no other hero has the strength to face the rising tide of villainy in the world? The situation is more perilous than ever, and that may be why One For All's embedded Quirks are emerging.
Whatever the reason for all this, Izuku, Bakugo and All Might agree that this collection of Quirks inside Izuku is remarkably similar to how the All For One Quirk typically works, collecting other users' Quirk factors and assembling them inside one body. The main difference is that Izuku is not doing this on purpose -- even if he could, he would never willingly steal someone else's Quirk. Instead, he inherited them, since the previous users imprinted their natural Quirk factors into One For All over time (though All Might didn't have one to imprint). Thus, One For All has seven bonus Quirks in it, giving Izuku a potential total of eight. Only All For One and Nines have ever been a walking collection of Quirks like that.
Not only is One For All becoming oddly similar to its nemesis All For One, but they even have similar origins. Generations ago, the villain All For One was dismayed at how sickly and defiant his brother was, so he forced a power-storage Quirk on him to keep him healthy. Over time this Quirk became One For All, and the original wielder resolved to strengthen it until it could take down All For One at last, sometime in the future. Sure enough, later wielders kept charging it up and added their own Quirk factors to it, with the recently revealed Blackwhip being only one of several. Ironically, defeating a deadly collection of Quirks calls for a hero who does the exact same thing. The main difference is, of course, that these bonus Quirks were inherited as a heroic legacy rather than stolen as weapons of war.
This is the legacy Izuku inherited, and recent events such as his dreams and the emergence of Blackwhip make it clear that the legend is entering a new phase. All For One and his fellow villains are this close to conquering the world of My Hero Academia, and no other hero, not even the mighty Endeavor, can stop them.
The fabled time is now: Izuku must harness the true power of One For All to take down All For One, and the only thing that beats a Quirk amalgamation is, well, another one. Izuku has no choice but to fight All For One on equal terms and hope that his heroic resolve, combined with his own Quirk collection, can topple the greatest villain the world has ever seen.