Robin Sena is a "craft user", born in Japan and raised by the Roman Catholic Church in Italy. She is trained to use her craft of fire to hunt down witches. Witchcraft is a genetic trait, dormant within a number of individuals within the human population. Powers can be "awakened" in these dormant human "seeds" at any time, which seems to also drive the awakened witch into various forms of homicidal madness or sociopathy. Trained hunters, craft-users or "seeds" themselves that have not become full witches, are needed to keep watch over "seeds" and hunt those whose abilities become active, serving in secret organizations, such as the parent branch "Solomon" and the "STN-J" branch in Japan, as self-appointed witch police to curtail the use of witchcraft in society, and to keep the witch kind a secret from the public. Even the police, who cooperate with STN-J in abnormal criminal cases, do not know what STN-J does.
