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 (fire) to hunt down witches. Witchcraft is a genetic trait, dormant within a number of individuals within the human population. However, powers can be “awakened” in these dormant human “seeds” at any time.
Trained hunters, usually craft-users or “seeds” themselves, are needed to keep watch over “seeds” and hunt those whose abilities become active, serving in secret organizations, such as the parent branch “Solomon”, as self-appointed witch police to curtail the use of witchcraft in society, and to keep the witch kind in secret from the public. Even the police, who cooperate with STN-J in abnormal criminal cases, do not know what STN-J does.