Bâo-Lèi Sword

The Bâo-Lèi Sword is a silvery sword and the most treasured heirloom of the Tao Family.

About
It posses spirit refining abillities and was able to evolve Bason from a Human Ghost, to a Seirei Class spirit by merely beeing used as a medium for the Over Soul

Anime/Manga Difference
In some translations it is known as Hou Rai Ken(Jewel Thunder).