Is demon guaranteed after a blocked crouching tick? Ie, crouching short (blocked) demon? They have to have crouched to have blocked it, after all.
As to why Akuma kills Zangief? First off, think of Akuma as a better ST Ryu. All the things Ryu could do that made his matchup with Gief basically even in ST, Akuma can do better. Better grounded fireball recovery, better knockdown fierce fireball, just as good normals, faster-startup fully invincible dragon punch to beat ticks, and more damaging hurricane kick combos to beat spd/bear grab attempts. Frankly, I think Akuma beats Zangief on the ground.
Second, whenever Akuma corners Zangief, the round is over. At the range where Akuma’s jab air fireball hits Zangief’s feet, Zangief can do nothing. He can do green hand, but if he does, Akuma recovers first, and Akuma gets a free knockdown combo into air fireball trap. Gief can also roundhouse bear grab under a fireball, but again, Akuma recovers first and gets a free combo into knockdown into air fireball trap. And the thing about this is, it’s not even that hard for Akuma to put Zangief into the corner. Virtually all of Akuma’s combos throw his opponent a huge distance backwards, so if he ever gets a hurricane kick or dragon punch or fierce fireball, Zangief is almost or actually is cornered.
Third, raging demon kills Zangief. Wanna lariat 1/3-1/2 a screen away from Akuma in expectation of a fireball? Boom, demon eats lariat for free. And Gief has no way to escape Akuma’s air fireball-demon trap, which is where Akuma jumps in with an air fireball that goes just over the opponent’s head and does demon on landing; Gief’s only way of escaping the demon is to jump into the air fireball. Because Akuma has no hitbox while in demon, demon always beats spd ticks, and reversal spd always loses to demon ticks. When Akuma jumps in with regular air fireball, he can either do a low attack xx combo or do raging demon; if you expect demon, you hold up to jump, and if you expect low attack, you hold down, but demon beats holding down and low attack beats holding up. Either way, Akuma is safe, and Zangief has no way to get himself out of this bad situation other than guessing correctly.
Don’t even bother with teleport, it loses to too many things.
So what do you guys do after you land demon and you’re standing right next to your opponent? I usually do meaty jab dragon punch. Beats whatever they have outside of super or Ken/Akuma strong dragon punch, and you’re safe after you do it against most characters. Against the characters I’m not safe against, I do jumping away/toward hurricane kick (away if I’m not cornered, toward if I am).