D² is extracted from the substance of the Bira (ビラ, Bira) tree, which NGL holds 80% of this species of plant. The distribution of the drug is mostly through Gyro's henchmen. The effects of the drug are unknown.
This drug developed by Gyro was only the beginning of his broader plan to disseminate evil throughout the world.
After the Gyro's departure, the NGL having fallen into the management of the International Peacekeeper Force and being designated as a nature reserve under the jurisdiction of the Hunter Association, the production and distribution of the drug most likely stopped.