The Protection Sword (known as the Goshinken) is an specially-forged, ages-old sword with writing inscribed on the blade. It is a tool of the Tsuchimikado Family.
By absorbing the aura within the user's body, it becomes capable of withstanding and repelling even a Tsuchigumo with a single swing in its initial state.
In the anime, by invoking the blade with an incantation and blood, the blade becomes imbued with the power of Sakra and is capable of using powerful blue flames. However, as demonstrated by Harutora who wielded this weapon, these flames can be difficult to handle at times.
Incantation: "Praise be the Buddhas, far and wide! Praise be Sakra, I call upon thee!"