In fact, this impression wasn't wrong. She had already been ill when he had first met her. Also, what she had wasn't an ordinary illness, but a cursed disease that the medical world couldn't figure out. In terms of Eastern context, it was like some voodoo spell that was cast using a mirror and a sword, and in Western context, it was a magic that was 'similar to a curse'. However, it didn't matter what they called it; basically, this woman was in a condition where there was no cure for her, and she could die any second.

[...]

However, he just needed one. The name of that grimoire was 'baopuzi'. In Chinese culture, it was a grimoire that was said to teach people how to be a 'deity' and live an immortal life. It should have a record of what was called 'alchemy'; in other words, it had a method of creating an immortal elixir that could heal any disease or curse.

Toaru Majutsu no Index vol.5 ch.4 pt.9,15