Arm gets cut off result

“You bastard. You weren’t thinking that you could crush my Imagine Breaker just by
cutting off my right arm, did you?”
He bared his teeth, his eyes with such a glint that they might have fired red light from
them.
The boy spoke, sincerely delighted.
(Wha— Wait, don’t think unease ba—)
Aureolus was able to pray, but he wasn’t able to stop thinking.
In that instant...
That hole, left by Kamijou’s missing right arm...Something strange happened to the flow
of fresh blood erupting from it. Something unknown, something transparent, slowly
began to show its form, like scattering blood on a glass sculpture.
Something leaped out of the hole in Kamijou’s right shoulder then, and it was certainly
not a human arm.
It was a jaw.
It was like nothing he’d ever seen before, save in legends, for it had a length of more
than ten meters and a ferocious brutality. It was the gargantuan, gigantic jaw of a
dragon king—also called Dragon Strike.
He should not have been able to see it, for it was transparent, but it was covered in blood.
As if it were the boy’s own arm, he slowly opened its mouth, lined with fangs like saws.
As if he was saying that this was the true form of the power packed into his right hand.

One of the fangs made contact with the air.
Nothing particularly large changed. However, something he couldn’t see had definitely
been altered. Though the alchemist’s presence had been filling the room, it vanished, as
if his very initiative, the ownership of this area, had been modified.
(Wha...)
Aureolus looked up in spite of himself to the distasteful planetarium of human flesh,
created with Stiyl Magnus’s skin and blood. The carnage spread about the room began to
slither toward one point...as if his order had been canceled.
(It...can’t be. He is coming back? The same as Himegami, who I already destroyed—!)
The moment he thought that, Stiyl dropped to the floor, not a scratch on him.
Icy fear stabbed into Aureolus’s back.
Without a doubt, his own insecurity had revived the magician.
(Wait, this is no more than my unease, calm down, erase unease and I can erase this
ridiculous thing—!!)
Desperately biting down on the terror about to claw out his heart, Aureolus attempted
one last resistance. This scenario should have been no more than something created by
Aureolus’s own misgivings. So if he calmed himself down and got rid of this anxiety, the
strange power in the boy should also disappear.
But the light of the transparent dragon king’s shining eyes was brought to quietly glare
at him.
That was all it took to give Aureolus the illusion that his vision was fading from terror
alone.
(I can’t...There’s no way...)
Immediately after thinking that, the jaw of the dragon king opened as wide as possible
and devoured the alchemist from the head down.

- Toaru Majutsu no Index Volume 2, Chapter 4 Part 2