Foil
Character Role Analysis
Hermine and Harry
Hermine is pretty much everything that Harry isn't: happy, young, healthy, and open to new experiences. All those differences show us just how unhappy, old, unhealthy, and closed off our hero is.
However, this is a special foil relationship (kind of like the one between your fillings and aluminum foil) because the two characters are very different, but Hermine also seems to come from within Harry—he makes up her name, thinks that she is his old school friend Herman, and when he kills her in the Magic Theater it seems more like an action against himself: a suicide mission rather than a murder.