[Evidently Tidus is not on the list of people he's explained his magic to. How had he missed that?]

No - my magic requires skin contact. I connect my life to my patient's and use it to heal them. It doesn't hurt me normally, but if the connection is broken or I try to help someone who's too far gone, it could kill us both.

[Very powerful but very delicate.]

So like I said, trying it on a god is risky, and I don't want to try it when there are other ways I can heal them.

[And now Tidus has a slightly more detailed explanation as to why Ryo didn't try his magic on Zagreus after the mission.]