Ritual sacrifice

Invoking a supernatural creature? Closing a portal that should have never be opened? Opening a portal that should never be open? Looking for a boosting of power?

No matter which, only that someone will end up being used as a tool for it, and the implications of this are... whumpy.

Might lead to death, and might be a case of self-sacrifice.

Animes
Ao no Exorcist


 * 1x22/1x23: After being imprisioned, Rin is strapped to an X cross and used on a ritual to open the gates of hell. Screaming in pain, bloody, and being watched by a worried brother, who offers himself to take that role.

TV Shows
Merlin


 * 1x07: Arthur (Bradley James) is controlled by a magical being, and almost drowns on the lake, as a sacrifice to open the gates of Avalon.