Brandon, the protagonist, is a highly-trained special agent.
Astrith, the other protagonist, doesn’t do anything other than… not dying.
It is a law of this universe that she cannot die. She doesn’t dodge bullets. Bullets dodge her.
A nuclear missile is a different story though. To save the world (except our immortal protagonist) from being obliterated, and to retrieve a mysterious stolen casket, the duo set forth a journey…

Dialogues in the game. Not a very good explanation of quantum immortality.

Where are you mortals aiming at? Not the immortal me!

Illustration in the game.