Vassal Axe

The Vassal Axe or Seven Star Axe, also known as the Axe Spirit of the Vassal Weapon. The spirit is from another world prior to being summoned to another world, the Vassal Axe is one of the eight Vassal Weapons present in the world which Naofumi currently resides in. The candidates of the weapon have been given the title of Axe Hero, whom they are generally addressed as so by the locals.

Overview
The Vassal Axe originates from the Sword World and is vassal to the Legendary Sword along with the Vassal Gauntlet. The specific role of the Vassal Axe in this trio has not been stated.

The Vassal Axe was first seen in the possession of Takt as he had collected all of the Vassal Weapons during his conquest for world domination. However, since he had so many weapons, he was unable to use each of them effectively. Takt was then defeated and stripped of the Vassal Weapons by Naofumi's authority. The Vassal Axe was not seen again until it was recaptured by the vanguards of the waves and suppressed. Mald was given this corrupted weapon and used the curse series without any side-effects. He and Miyaji were defeated but S'yne's Sister saved Mald before he had lost his Vassal Axe.

Power-up Method
The power-up method for the Vassal Axe is called "muscle enhancement". It is hypothesized to be a physical enhancement but the details are unknown.

Trivia

 * In the Web Novel, the Vassal Axe was first given to Filo. However, since Filo held both the Vassal Claw and Vassal Axe, she gave the Vassal Axe to Green.