As of December 2018, the Omni Arcanum no longer drops the materials in order to craft the Sphere "Tempest of Akachi". Instead the following materials will now be available to exchange in the Event Bazaar in exchange for Omni Arcanum Tokens:
Veiled Drop - 60 Arcanum Tokens
Occult Fang - 35 Arcanum Tokens
Mystic Stone - 50 Arcanum Tokens
Psychic Eye - 70 Arcanum Tokens
Note: These materials are required for solely crafting Tempest of Akachi.