It follows STNJ, a Japanese branch of a secretive global organization that fights the harmful use of witchcraft. Being a witch is a genetic trait, and STNJ maintains a database of everyone with the trait and moving in to eliminate/arrest them should their powers awaken.
Recently STNJ lost one of its members. Headquarters sends 16-year-old Sena Robin. A witch who was born in Japan but raised in an Italian convent. Robin's ability is Pyrokinesis.
Initially, the series appears to take a monster of the week approach. Around episode the characters, and their relationships are established. At that time, the real story gets underway.
As the series goes on, Robin grows increasingly uncomfortable with her role in hunting witches. Some of the witches do not deserve the punishment that they receive from the mysterious Factory, and eventually Robin begins to worry that she will become a target, and grows to suspect that her partner Amon will welcome the opportunity to hunt her.
This series is like a cross between Vampire Princess Miyu and The X-Files.
Witch Hunter Robin is debuting on Adult Swim on Monday, February 16, 2004.