while holding back he beats up a little girl

“If you don’t try to avoid this with everything you have, you really will die!”
As he yelled he struck with his left hand. The strike was gentle like he was stroking her
cheek....and yet a cracking noise came from Misaka Imouto’s neck upon receiving the
attack. Her vision spun around as her entire body spun like a bamboo copter before
landing on the gravel.
His attack did all that, but he had actually been holding back.
If Accelerator had seriously been trying to kill her, her body would have exploded the
instant he touched her skin.
“Now for a question. How many times have you been killed!?”
As Accelerator gave a broken-looking smile, he looked like a darkness hanging over her.
The smile splitting across his face filled her vision.
Something like a jeer came from his mouth that was opened so wide that drool was
about to spill out.
Accelerator had regained his utter advantage. Misaka Imouto was balled up on the
ground, but the tip of his shoe weaved through the gaps in her defenses and stabbed into
her. His fist flew and struck her on the back. With each strike, he was holding back
enough that her body would not be destroyed.

She was thrust into a spiral of intense pain as if she had been thrown into drum that was
being repeatedly hit with a metal bat from the outside.
“Ghfh...!?”
Misaka Imouto was having trouble even remaining balled up and she finally lost to the
force of a kick to the gut. She collapsed face up on the ground. Her forehead must have
been cut because she could not see out of one eye due to flowing blood. She could see
Accelerator breathing erratically in her blurry vision. He wiped away the drool that was
flowing down from the smile splitting across his face.

- Toaru Majutsu no Index Volume 3, Chapter 4 Part 5