The person’s scent and the feel of the person’s skin were both nostalgic. But something was wrong. It was like the difference between someone who was sleeping and someone who was dead.
[...]
“The difference between living and dead is a subtle one.”

“So we have new member of the Einherjar.”

It was an almost identical technique to the human modifications Marian carried out. Except this one specialized in corpses. Gold was put into the important parts of the human body and the corpse could be controlled without it decomposing.

Toaru Majutsu no Index New Testament vol.4, "profound destruction"