He was originally researching the illusions that appear to people when they were about to die. During this process, he managed to research how to stop a heart safely and how to restart a heart that was stopped safely. In terms of the outcome, he had the ability to revive people. But he was a man who was legendary even among the Kiharas because of his ability to control the number of times he could stop a person’s heart.

Toaru Majutsu no Index New Testament vol.4 sub 22