Why would the hero killer cut down the one person he regards as the pinnacle of heroism? Because All Might isn’t dead.
Stain is crazy. Obvious, but I’ve read my share of My Hero Academia fans agreeing with him and want to make that clear. So, let’s start there–Stain is goo goo g’ joob. He is not someone to easy deviate from his core ideology, and, in my opinion, All Might not sacrificing his life to save innocents will be unforgivable to Stain. A hero retiring? Living out their days away from the never-ending war on justice? Essentially, giving up? The All Might giving up? No. Dying in the field is how heroes retire, Stain will expect no less from the number one hero.
But, Stain is in a maximum security prison, the Tartarus. He’ll never be free, you say. Sorry, but even if you disagree with my Stain killing All Might theory, most of us can agree he’s not spending the rest of the series in prison. Granted, it may be a while before he reenters the story because of the impact that will have on the world, but it’s happening.
Assuming All Might will be murdered in Sir Nighteye’s prophecy, who better than Stain to do it? Okay, there’s Shigaraki and his presumed past with All Might not saving him as a child, but from the USJ arc, we know Shigaraki is willing to let someone else kill All Might as long as the deed gets done. Stain could waltz in Villain Alliance Headquarters and demand to be the one personally taking that ultimate pretender’s head. For all we know, it could all be part of Shigaraki’s plan. What better way to usher in a new society by killing the representative of the old with the hands of its biggest proponent?
In the end, it all comes down to Shigaraki. He’s already gone far using Stain’s warped ideology to recruit the best people to help carry out his goals. Will he take the next step and bring Stain himself into the fold? Or, does he even need him, letting the hero killer rot in prison? Either way, All Might better finish writing his will. Hope he leaves me his Best of Sade CDs.