WARNING: The following contains spoilers for My Hero Academia Chapter 346, "Super Hyper Unfair Broken Stage,” by Kohei Horikoshi, Caleb Cook, and John Hunt, available now in English from Viz Media.
The latest My Hero Academia chapter dived straight into the battle set up for Shigaraki Tomura. It revealed the elaborate plan the heroes had concocted specifically for the young harbinger of destruction and pit him against some of the toughest Pro-Heroes the story's introduced so far. Unfortunately, all these advantages were just barely enough to give the heroes an edge as Shigaraki's body, which has been months in the making, is finally complete - and it's terrifying.
While fighting the Pro-Heroes, Shigaraki quickly discovered that the wealth of Quirks at his disposal had been rendered effectively useless. At Jaku, he'd found Eraserhead's Quirk, the ability to remove someone else's within his eye line, the most troublesome of all. Shigaraki severely injured Eraserhead back then, taking away his ability to use the Quirk but unfortunately for him, the UA teacher survived and with him Erasure itself.
Teamed up with Monoma Neito, the Phantom Thief, Eraserhead brought Erasure back into play. By staying close to Monoma's side, they are able to subvert the five-minute limit of his Copy Quirk. Just like in the previous battle, they turned Erasure on Shigaraki and succeeded in preventing him from using his Shock Wave attack. Erasure worked but Shigaraki's immediate next move showed that it wouldn't be as pivotal during this battle as it was in the last.
Once he discovered he didn't have access to his Quirks, Shigaraki revealed his latest new ability. Apparently, the heroes weren't the only ones who powered up during the brief respite between conflicts because now, Shigaraki seems capable of augmenting his body as he sees fit. This strange power hasn't been explained yet but it looks like Shigaraki is now able to change the make-up of his body at will. He replaced his left forearm with a giant mound of flesh, which he used to push Mirko away easily.
All signs point to this new ability being the completion of Shigaraki's body that All For One eagerly awaited. It was first teased back in Chapter 341 when Spinner noticed a misshapen mound of flesh morphing back into Shigaraki. All For One explained it away as his charge conquering the Quirk Doomsday Theory. If true, that could mean the Shigaraki currently battling Pro-Heroes at UA has fully transcended the level of regular Quirk wielding humans. His fight with Star and Stripe proved he was in full control of the Quirks in his possession. This new technique might be some sort of physical manifestation of the many different Quirk factors still housed within him. Visually, it fits within Shigaraki's "handsy" theme as his body modifications look like they're made up of countless fingers.
It's clear that this ability in and of itself is not a Quirk. It works just like Shigaraki's increased durability, strength, and speed as none of those are affected by Erasure either. All these buffs make it clear exactly why All For One wants full control of Shigaraki's body. The duo has been working well together for quite some time but from how Shigaraki admonished himself to not get in his own way, their partnership must be fragile. Shigaraki Tomura in control of this massive power is bad enough but should All For One manage to get his hands on it, it'll be game over for the heroes.
