Warning: contains spoilers for My Hero Academia chapter 316!
As the most recent chapters of My Hero Academia have unfolded, Deku's latest opponent, Lady Nagant, has quickly grown into a popular character. With a complex backstory that shattered the image of hero society, her motivations for working with the deadly All for One were perhaps some of the most understandable among all the villains seen so far.
But as is the fate of the majority of villains, her battle had to end some time, and with an impressive display of prowess, Deku secured victory. Rather than arresting her, however, Deku took the opportunity to offer the relatable mercenary a chance to come back to the side of the heroes. He seemed to be successful in winning her over, but it was suddenly revealed that All for One had placed a fail-safe should she attempt to defect, and Deku was left facing a massive explosion. Whether she survived is as of yet unknown, but it's not looking good.
All for One provided Lady Nagant with a second quirk, Air Walk, but it seems that he slipped a third in as well: a self-destruct quirk, which can be activated under certain conditions, or in some situations even remotely. These self-destruct quirks have appeared before, in the hands of the so-called "Bomber Villains," created by the Villain Factory in Naruhata years earlier, as seen in My Hero Academia Vigilantes. The Villain Factory was eventually revealed to be a front for All for One, a place where his followers were experimenting with imbuing quirks and powering quirks up through the use of quirk-enhancing drugs such as Trigger. In many ways, the Bombers are similar to All for One's favored henchmen, the Nomu, as they have no personality, inhuman forms (some are winged, while others have several sets of arms), and are often equipped with more than one quirk.
It's known that the Villain Factory's most successful creation, a being known as Number Six, possesses a quirk which was directly stolen by All for One, so his involvement is easily confirmed. It's also known that with the help of Doctor Garaki, creator of the Quirk Singularity Theory, All for One has been able to "clone" quirks, allowing him to keep the original while still passing abilities on to his followers. It's likely that All for One still possessed the self-destruct quirk after offering it up to the Bomber villains, and took this opportunity to pass it on to someone he suspected might betray him.
The Bombers, with no personality or desires, were unable to disobey and so followed directions to explode without concern. Since it's clear Lady Nagant would not have self-destructed willingly, it's possible that All for One either set up a particular set of conditions (say, for example, if she failed to assassinate Deku), set a deadline that would destroy her after a certain period regardless of her success, or had someone tailing her (other than Chisaki) with the ability to activate her self-destruct should she appear to be considering betrayal. Exactly which of these is the case remains to be seen, but if she was being followed, then Deku's not out of the woods yet. There is a ray of hope, however: the Bombers' bodies were destroyed, while Lady Nagant's seems charred but intact, and Hawks managed to catch her as she was falling. If Deku and Hawks can get her to a healer quickly enough, the popular assassin just may live to appear in future chapters of My Hero Academia.