In the Secret Wars, the Human Torch was being choked by Ultron, a robot completely encased in Adamantium. Obviously, fire doesn't do much against any metal from the Coolnamium family, so Torch went nova, so he would at least look awesome as he died. However, Ultron stopped. His shell was intact, but the nova flames melted something important inside him. I think that's what we're dealing with here. Alistair couldn't figure out how to crack Fujita's skull, so he simply hit it hard enough that everything in it turned to liquid.
"He said your Quirk was only shock absorption, not nullification. That means there's a limit to what you can take, right?! So, you were made to fight me, big guy. If you can really withstand me firing off at 100% of my full power, then I'll just have to go beyond that and force you to surrender!"
— All Might, My Hero Academia
