Instead, the portions that had been destroyed had become feathers of light that were as pure a white as the pillar of light. They floated down. Kamijou had no idea what effects they might have had, but a few dozen of those feathers of light came floating down like winter snow on that summer night.

[...]

At that moment, one of the feathers of light fell down on Kamijou Touma’s head.

[...]

Kamijou fell down and covered Index who was still collapsed on the floor.

It was like he protected her body from the falling feathers of light. The dozens of feathers of light floated down like snowflakes towards every part of Kamijou’s body.

Even so, Kamijou Touma smiled. He smiled and he never moved those fingertips again.

On that night, Kamijou Touma “died”.

[...]

“Your memories were ‘killed’, brain cells and all.”

What a ridiculous thing for me to say, thought the doctor.

But, he continued.

“To liken the human body to a computer, your hard disk was utterly fried. If there’s no data left in your brain, just where are these memories supposed to be?”

Toaru Majutsu no Index vol.1 ch.4, epilogue