The target merely stopped their own heart because it would be better than being hit by the full power of the blade. How was one supposed to stand up to an attack on that level?
No physical projectile came from the sword.
It could not be evaded if you were quick enough or blocked by hiding behind cover.
No matter where you ran or what you did to defend, the fear welling up within your own body would automatically kill you. So you could not run. You could not defend. Nothing you did held any meaning. You were dead before you could do anything. You were dead the second you stood on the same battlefield.
All actions were robbed of all meaning.
All fighting lost its reason to exist.

Toaru Majutsu no Index New Testament vol.4 ch.n pt.1