Man, this question has been bugging me ever since I caught up with 'My Hero Academia.' The mystery around Deku's dad is one of those lingering plot threads that keeps fans theorizing like crazy. From what we've seen in the manga and anime, Hisashi Midoriya is barely mentioned—just a quick reference to him working overseas with a fire-breathing Quirk. But here's the thing: One For All is such a tightly guarded secret that even most pro heroes don't know about it. All Might kept it under wraps for years, and Deku only learned the full history gradually.
Personally, I doubt Hisashi knows. If he did, there'd probably be some hint—a letter, a cryptic comment, anything. The fact that Deku's mom seems clueless makes it even less likely. Plus, All Might emphasized the danger of spreading that knowledge. Still, part of me hopes we get a twist where his dad secretly knew all along and shows up with some wild backstory. Imagine the emotional payoff!