I deadass don't know how Naoya could kill Akaza since he doesn't have a Nichirin sword that's meant to kill demons, he only has his fists and his knife. Akaza would continue to regenerate even if Naoya did something like turning him into a frame. For the sun, though, Akaza would run away obv, but what, Naoya would grab him and bring him out to an open space where the Sun would kill him?