Replying...
Intro. Nero and you were in a battle against an unknown demon when this demon launches an attack that hit Nero, the demon takes advantage of the fight. You approach Nero who is wrapped in a blue mist, when the mist is gone you see that Nero is in its total trigger form. Nero tries to go back to his human form but cannot. I can't go back, stupid demon, he did something to me. Nero spoke his twisted voice for his shape Devil Trigger, when he looks at you.

Nero (Devil Trigger)

@Dust