My Hero Academia's current arc may be more focused on the students training with one another, but something has been brewing in the background for a while as the manga laid out more clues as to how One For All works.
The series may be setting up for an even greater One For All surprise as All For One teases that he might have a deeper connection than first teased.
All For One once passed on a quirk to his younger brother, who was originally thought to be quirkless, and that power grew to be what's now known as One For All. Midoriya saw this all happen in a dream shortly before the current arc of the series began, and it filled in the blank of what eventually went down between the two brothers as All For One grew into his currently menacing self.
This "Vestige" was teased to be an effort to contact Midoriya from All For One's younger brother, but things were cut short as they passed the point of "singularity" and Midoriya still doesn't have full control of One For All. But in the latest chapter, it's suggested that All For One shares this "Vestige" power as well.
At the end of the chapter, All For One (still locked within Tartarus after his fight with All Might) mentions that he's feeling nostalgic and can hear his little brother's voice. It would make sense that he could be using this "Vestige" power as the two share similar quirks, and All For One's boost to his brother is what started it all in the first place. But this makes this especially worrisome for Midoriya, who not only has to deal with All For One now, but still defend himself against the League of Villains, and figure out the last remaining secrets of One For All before it's too late.
My Hero Academia was created by Kohei Horikoshi and has been running in Shueisha's Weekly Shonen Jump since July 2014. The story follows Izuku Midoriya, who lives in a world where everyone has super powers, even though he was born without them. Dreaming to become a superhero anyway, he's eventually scouted by the world's best hero All Might and enrolls in a school for professional heroes. The series has been licensed by Viz Media for an English language release since 2015.