Season 5 of My Hero Academia has been a long series of all-out brawls between our usual protagonists in U.A. High School's Class 1-A and the consistently sidelined heroes of Class 1-B. Meant as a practical training exercise, this Joint Combat Training has been a chance to see plenty of new Quirks in action for the first time, as well as for us to see new developments from all of our favorites. Between things like the fruits of Ida's Quirk training and Bakugo's newfound maturity, it's been interesting to see the ways the heroes in training have grown.
No one was prepared, though, for the biggest surprise of all: in the final round of training, Izuku Midoriya seems to have accessed a new power entirely.
Midoriya began the series by inheriting the powerful Quirk One for All from All Might, and he has been training to get it under control ever since. Where he once couldn't use One for All without causing himself great harm in the process, Midoriya has come a long way, learning techniques like Full Cowl and the finger-flicking Delaware Smash to lighten the collateral damage of his Quirk on his body. However, in Episode 98, “That Which Is Inherited”, Midoriya inadvertently discovers a surprising part of his Quirk that not even its previous inheritor All Might saw coming, and it will require a whole new kind of training to master.
As it turns out, this new power is an entire Quirk of its own named "Blackwhip". We know this because, while he is sent to the inside world of All For One where the spirits of the previous owners reside, Blackwhip's original user appears to Midoriya and tells him a bit about it. According to Blackwhip's user, his Quirk has been quietly folded into - and gaining power from - One For All's "core". And it's not the only one: every natural Quirk from Midoriya's predecessors lies dormant inside One For All, potentially giving Midoriya access to six new powers in total.
Blackwhip takes the form of tendrils of dark energy emanating from Midoriya's body. When unleashed, these tendrils spread far enough for everyone participating in the training to see, and violently snap back and forth, easily causing destruction to the training grounds around him. Blackwhip also seems able to latch onto things, at one point keeping Midoriya suspended in mid-air after the tendrils stop moving and tense up, still attached to the various walls and pipes of the battlefield. All of this is quite dangerous currently, as Midoriya seems to have no control over Blackwhip, and if he hadn't been calmed down by Uraraka and Shinso, he would have likely put all of his friends in harm's way.
However, Blackwhip's original owner believes this development is actually a good thing. Midoriya accidentally accessed Blackwhip when chasing Monoma and wishing he was more easily able to catch him, so it is likely that One For All was simply trying to help. Blackwhip's user believes this, too, saying his Quirk was the best solution for the situation. When demonstrating his own usage of Blackwhip, it is much more calm and small, taking the form of only a handful of tendrils in his palm. If that's what Midoriya was working with, he probably could have used Blackwhip to ensnare Monoma and end the fight easily.
That isn't how things went, though, and that discrepancy tells us a lot about what Midoriya's training will look like from here on out. Midoriya’s Blackwhip is much stronger than its original form thanks to its time inside One For All, so it will take some time to master just like One For All did from a physical perspective. More importantly, though, Blackwhip's owner tells Midoriya that Blackwhip's power is tied directly to the intensity of its user's emotions. Anger is a good thing, he says, but Midoriya must be in control of that anger, lest he lose control of Blackwhip.
That means that Midoriya will need to start focusing on his emotional strength more than ever before, which is an exciting development for him as a character and a hero. When it came to One For All, mastering his Quirk largely meant training his body to withstand his immense strength. Now, though, Midoriya will need to work on his mental fortitude, learning to embrace his emotions without letting them control him. No more rage-filled rampages that end in visits to Recovery Girl's office - Midoriya will have to master his body and his mind to save the day from now on. It's an interesting development for our fledgling hero, and it will be fun to see My Hero Academia move on to a totally new chapter in Midoriya's character arc, finally rewarding him for growing on the inside and the outside.