Vassal Hammer

The Vassal Hammer  or Seven Star Hammer, also known as the Hammer  Spirit of the Vassal Weapon. The spirit is from another world prior to being summoned to another world, the Vassal Hammer 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 Hammer Hero, whom they are generally addressed as so by the locals. The current candidate of the Vassal Hammer is unknown.

Overview
The Past Heavenly Emperor also known as Raphtalia's Ancestor, seems to have wielded a similar weapon in description of the Vassal Hammer, however, there's no solid proof whether the hammer that she has in her possession is the Vassal Hammer.

A few days after the four Legendary Heroes were summoned, the Hammer Hero went missing. It turns out that this Vassal Weapon wielder was killed and had the Vassal Hammer taken. The Vassal Hammer was next seen in Takt's possession during his campaign to take over Raphtalia's World. However, since he had collected all of the Vassal Weapons, he was unable to use any single one effectively. Eventually, Takt was defeated and Naofumi used his authority as a Holy Hero to strip Takt of his Vassal Weapons.

Power-up Method
The power-up method for the Vassal Hammer is unknown.

Trivia

 * In the Web Novel, Raphtalia wielded the Vassal Hammer.