doesn't cut off a hand despite it punching her sword

As the strikes glowed blue in the moonlight, the skin of one finger on Kamijou’s fist
lightly touched them.
And was eaten into.

“Wha...!?”
It did not disappear. Even with Imagine Breaker, those absurd strikes did not disappear.
Kamijou immediately tried to yank his hand back, but he did not make it in time. After
all, he had stuck his own hand into the oncoming strike of a Japanese sword.
Kanzaki narrowed her eyes slightly at the sight of Kamijou.
In the next instant, the wet sound of flesh being sliced apart filled the area.
Kamijou held his bloody right hand with his left and fell to his knees.
He was honestly surprised to find all five of his fingers were still attached.
This was of course not due to Kamijou’s fingers being tough or Kanzaki’s skill being poor.
Kamijou’s body had not been sliced to pieces due to the simple fact that she had held
back, held back some more, and allowed him to live.

- Toaru Majutsu no Index Volume 1, Chapter 2 Part 4