A supernatural weapon, presided by a certain god.
Calling / urging a certain world to call or use the necessary knowledge of an astra, when armed. Invited gods make it impossible to change the weapon regularly. The existence of certain conditions involves the use of ostrous, which can be fatal in violation. Because of the involved power, the knowledge involved in an Astra is passed by the word of the sole-word of the Guru-teacup to a disciple (student) from a guru (teacher), and only following the founding of student character. Certain astras were directly transferred to the gods involved, the initiation being inadequate knowledge.