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Vassal Items (眷属器), commonly known as the Seven Star Weapon (七星武器), are a collection of eight items which are derivatives of the Four Legendary Weapons. "Seven Star Weapons" is a nickname for all of the vassal weapons. Since there are seven known weapon the grant a person status of hero, its called "Seven Stars". Although the Legendary Carriage would consider as seven star weapon, since its lack of publicity caused many to think its existence was a mistake and it faded into obscurity. Those who possess a Vassal Weapon are considered heroes and are able to breach the level cap. Although the Four Saints are only chosen from otherworlders, the Seven Star Heroes can be selected from any individuals. The Gauntlet was the last weapon of the Seven Star Weapons to choose a user from the current generation.
Much like the four Holy Weapon (聖武器), Vassal items are able to absorb items to unlock new variations of itself or to recreate itself in the appearance and ability of weapons of the same category. Strengthening method is unique to each item, since help menu only explains one method for each item. But if the user truly believes the item can be strengthened through other methods, new strengthening methods are unlocked.
Originally, each world has only One Holy Weapon and Two Vassal Weapons. By the time of Naofumi's summoning, there were a total of 4 Legendary Weapons and 8 Vassal Weapons. After the Fusion, there was a total of 8 Holy Weapons and 16 respective Vassal Weapons to those 8 Legendary Weapons.