Demon Eye Wash

Demon Eye Wash is a form of eye drops that is used to cure one from being able to see demons.

Synopsis
Mephisto Pheles reveals the eye wash to Rin Okumura, seemingly knowing all about Sei Godaīn's plight and of Rin's determination to find a way to help him. He offers it to Rin, but on the condition that he will not receive it until after completing an assignment.