The Mageste is a weapon exclusive Annest Miguell. It is a Mace that doubles as a Horn. It is considered a Pseudo Weapon for that feature. It is available for her use after the Grandmother's Heirloom side-chapter of Chapter II, Audacity.
Mageste is a megaphone-like, conch hybrid horn that is technically a Musical Instrument of the Horn class, but is also durable enough as a mace for it club-like thickness.