Gourd of Purification is an ancient instrument of the gods.
Legend says that it is an incarnation of a deity and a demon. In the day, it's known as an instrument of purfication, and can be used to heal all sorts of illnesses. On the other hand it turns into an instrument of evil at night. As it is an instrument of both good and evil at the same time, it should never exist on the surface of the earth for it may bring forth great calamity.