Midoriya Izuku, aka Deku, was destined to use all seven of the Quirks of those who came before him in My Hero Academia ever since he first inherited One For All. Deku started doing extra training after the catastrophe that was Blackwhip's first appearance to make sure he wouldn't ever be caught off guard again and to make the most of his new abilities.
He finally displays the results of his training and uses One For All to its full, terrifying potential in Chapter 369 of My Hero Academia.
How Deku Became a One For All Master
Since he was born Quirkless, activating One For All never came easily to Deku. Even after he learned its secret, he was wont to hurting himself by using more of the Quirk's power than his body could handle. This phenomenon repeated itself when Deku started unlocking other Quirks; activating them was a tedious process, and he had to be extremely careful in their use. Interning with Endeavor accelerated the process of mastering One For All, as the Flame Hero introduced him to the concept of parallel processes.
Endeavor compared the difficulty of mastering multiple Quirks to driving in order to make it easier for Deku to comprehend. No driver ever took their first turn at the wheel of a car knowing exactly how to control it. As time went on, they added more abilities, like using turn signals and checking their mirrors, so frequently that they eventually became second nature. Endeavor encouraged Deku to continue experimenting with Blackwhip and One For All's strength boost combinations since he had previously restricted himself to using only Blackwhip.
My Hero Academia Chapter 369 Shows What One For All Looks Like in Full Power
This long-term strategy appears to have paid off based on Deku's exploits in Chapter 369 of MHA. Not only is he using every single one of his Quirks in succession without any blow back, but in his true over-explaining fashion, Deku is able to give a blow-by-blow recount of exactly how his air of omnipotence is achieved. His narration reinforces the entire chapter's theme of single individual Quirks growing together to become a greater power, as All For One is forced to relive visions of his encounters with past users of One For All when he recognizes the abilities.
Each Quirk Deku employs after another demonstrates an uncanny level of synchronization. Each Quirk either directly translates into a setup for the next or perfectly complements the previous one. Deku is able to completely block out all of the visibility around him using Smokescreen, Danger Sense, Float, and Blackwhip while still having a perfect idea of where his victim is and more than enough means to get to them right away.
Gear Shift gives him complete control over his body's movements down to the cellular level, and when combined with One For All's brute strength in the form of a punch, he can land one that is exponentially more powerful than it would have been otherwise. Meanwhile, Fa Jin automatically restores as he moves, allowing him to use Gear Shift's Overdrive as soon as its first charge runs out.
Impressively, all of this force was not enough to make All For One despair. Instead, My Hero Academia's ultimate villain drew inspiration from One For All's theme of past actions paying off in the long run, thinking to himself that victory had not yet evaded him. Like he always did, All For One had set aside several pieces that could bail him out of a tough spot if need be. This time, it appears his trump card is Spinner.
The founding member of the League of Villains has been absent from the MHA manga ever since he was revealed to have accepted a Gigantification Quirk from All For One. Spinner has become a symbol of heteromorph freedom; with his newfound power, he is violently enforcing his ideals at a separate battlefield. Now, it seems the time has finally come for him to pay his due.
