WARNING: The following contains spoilers for My Hero Academia Season 5, Episode 11, “Our Brawl,” now streaming on Crunchyroll, Funimation and Hulu
Many Quirks in My Hero Academia require a specific set of circumstances for them to be appropriately activated -- Neito Monoma’s Copy is no exception. A major part of Monoma's plan was to use his Quirk to copy Deku's, but he knew there was the possibility of drawing a "blank."
My Hero Academia Season 5, Episode 11 saw the end of Class 1-A & 1-B's joint training battles as Deku's team went Plus Ultra to pull out the win. Still, Monoma's squad -- which included Shinso -- put up a solid outing themselves, and their plan could have worked if One For All's stored power had been copied. While Monoma managed to touch Deku and swipe One For All, it didn't grant him the Quirk’s trademark super strength.
After Uraraka and Shinso stopped Blackwhip’s rampage, Monoma took advantage of Deku’s dropped guard to sneak up on him using Yanagi’s Poltergeist Quirk. He managed to brush Deku, but Uraraka’s quick intervention forced him to retreat before he could cause any real damage. Monoma bided his time after that skirmish, but when he noticed Deku and Uraraka alone once again, he struck, this time going on the offensive. Unbeknownst to the two Class 1-A students, Monoma grazed Deku earlier and succeeded in copying his Quirk. After all, he’d shown up this time intending to use Deku’s own strength against him.
However, once Deku realized what Monoma was up to, he feared the repercussions One For All would have on Monoma’s ill-prepared body -- but he didn’t have to worry. After the Quirk failed to activate, Uraraka tackled Monoma without much resistance. She told Deku that Monoma was bluffing, but from his surprised reaction to the Quirk not activating, that didn't seem to be the case. So why wasn’t Monoma able to use One For All properly?
While Monoma’s Copy is a very impressive Quirk, it’s not necessarily the most straightforward. It allows him to copy the Quirks of up to four people he’s touched for 10 minutes. Though no Quirk is immune to him, some can't be entirely replicated or used to their full potential.
On top of One For All being a power stocking Quirk, it also houses the Quirks of previous users. The reason it’s so powerful with Deku is that it’s been passed through eight different users who spent years strengthening and adding to it before passing it on. Monoma copied the base ability of One For All, not the power it has been stocking. So, there wouldn't be enough time to build up enough meaningful strength with only a few minutes. A similar result would come from Monoma copying Fat Gum's Fat Absorbtion Quirk, which has a stockpiling prerequisite.
Monoma’s Copy allows him to replicate the effects of any Quirk, but he can’t immediately use Quirks that require their user to store up something beforehand. Instead, he’d have to go through the same process before effectively using it. Another Quirk that Monoma could have trouble with after copying is Tamaki Amajiki’s Manifest. This Quirk allows Tamaki to manifest the physical characteristics of anything he’s eaten within a twenty-four-hour period -- meaning Monoma would need to consume something to use Tamaki’s ability effectively. Every Quirk has its limits.
