My Hero Academia's Joint Training arc has taken a mysterious turn as Midoriya's One For All is acting much more volatile than it ever has before after he had a run in with the original wielder a few chapters back.
But the latest chapter hints at something much larger for Midoriya as he might even tap into different aspects of the One For All power he didn't realize before.
When fans were first introduced to the idea of One For All, All Might emphasized how it gathered the power of every single hero who wielded it before and that's why All Might was as strong as he was in his prime. Midoriya has been training to harness the power in the same way, but maybe he's been going about it in the wrong way. In Chapter 212 of the series, Midoriya's berserk One For All explosion quells and Midoriya meets another previous user of the power.
The new hero, who hilariously reminds fans of popular comic book hero Hellboy, says that Midoriya is "not alone" and chastises Midoriya for using the power "casually" and "all distracted." Which means that there's an aspect of the One For All quirk that Midoriya still hasn't tapped into. This dream he has meeting another Vestige implies that each of the previous wielders are still residing in One For All in some way.
This idea was hinted at as early as the Sports Festival arc when they helped Midoriya free himself from Shinso's brainwashing, but this latest development suggests that the previous wielders can have a much more direct influence on how Midoriya uses his quirk. This also implies that the bizarre lightning explosion was just another manifestation of his power, another way it can be activated.
Midoriya has only been boosting his strength and speed because that's what All Might did, but since One For All has gathered the strength of every other vestige before, perhaps it absorbed their Quirks as well? This could be a major shake-up to Midoriya's power repertoire that could be explored as the series continues.
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.