Wind Taker

Wind Taker is a dagger that absorbs the essence of beings it kills, using that essence to improve itself. When essence is absorbed, the dagger's physical form changes to match the essence it absorbs. Scholars assume this is because the dagger applies the stolen essense to the dagger's own sphere of Body, and not its other spheres(As a dagger doesn't have spheres of Heart or Mind). The essence stolen is then applied to a collective reservoir. Should the reservoir be destroyed, the essences will be released into the world.