Vassal Book

The Vassal Book is one of the Eight Vassal Weapons from Glass' World. The person who possesses the weapon is called the Book Hero. The book holds a blue gem that can absorb materials and the ability to transform into, presumably, other book-based forms.

The current Book Hero is Ethnobalt.

The former Book Hero was Kyo Ethnina.

Trivia

 * In the Web Novel, Marin wielded the Vassal Book.