Warning: Spoilers for My Hero Academia Season 6, Episode 9Shigaraki's new form and abilities in My Hero Academia may make him seem unstoppable, but Deku has already recognized a weakness in the villain, and it's the same one Deku had so long ago.
Obtaining the power of One for All wasn't easy for Deku in My Hero Academia; he had to undergo intense physical training to even be able to accept the power, and even then, every attempt to use it just left his bones shattered into a million pieces. It took a lot of special training and mental discipline to be able to use it the way he does now, and as a result, he's achieving a level of mastery over One for All that none of his predecessors have ever been able to do.
Shigaraki, on the other hand, was given All for One and then immediately put into a science-induced slumber, which was supposed to do all the adjusting for him. Since he was awakened too early, that method of preparing Shigaraki's body was incomplete. As they fought, Deku immediately noticed that Shigaraki's attacks and use of Quirks were having a direct negative impact on his body--just like what happened to Deku when he first inherited One for All. The power is simply too much to wield without injuring himself, and while Shigaraki might not care that he's doing that, every injury he deals to himself brings him one step closer to defeat. Shigaraki tried to take the easy way out, and as a result, he can't measure up to Deku.
Deku Can Exploit Shigaraki's Weakness
Knowing this does give Deku a serious advantage. If he can bait powerful attacks from Shigaraki, each missed attack will deal damage to his own body instead, and as Deku himself has learned, willpower can only get one so far by itself in the face of such injuries. Unfortunately for Deku, Shigaraki has already survived a Prominence Burn attack from Endeavor near the episode's end, and still remains on his feet, so to speak. Thoroughly charred, Shigaraki--or rather, All for One taking control of Shigaraki's body--is still able to use Quirks such as the Rivet Stab without regard to his injuries. It's not clear yet if this is because of All for One taking control; it's possible that All for One controlling him remotely is overriding the ability to feel pain, or that All for One simply isn't feeling Shigaraki's pain and doesn't care about it. The one flaw with that plan is that Shigaraki's body really can only take so much, even with regeneration, and may stop working if All for One pushes too hard past the pain. Surely that's not the fate he had in mind for his protégé, so he may be forced to stop in order to preserve Shigaraki's life.
Spotting a weakness is a big help, but there's still the challenge of actually making use of it, which will be no easy feat. As My Hero Academia's most desperate battle yet continues, it's all up to Deku to put his strategic mind to work and save the day.
New episodes of My Hero Academia are currently streaming on Saturdays via Crunchyroll.