"Drassil" is a term that refers to the alien organism that resides in the Harnessed of Magician's.
Powers and Stats
Origin: Gokukoku no Brynhildr
Attack Potency: At least Small Building level (Due its size)
Speed: Superhuman (Can easily catch humans)
Lifting Strength: Unknown
Striking Strength: Small Building Class
Durability: At least Building level (This is a giant monster with very tough skin)
Standard Equipment: None
The Drassil is an alien life form residing inside the Harnessed of Magician's. Regular administrations of Death Suppressants are required in order for the life form to survive. They are the source of a Magician's power.
According to Miki, the Drassil is the true form of Magicians and that their consciousness now resides in the life form rather than their brains. She further elaborates that they're no longer human, and that their personalities are simply reproductions recreated within the Drassil. If enough time passes and the Magician continues to take the Death Suppressants, the life form will eventually hatch, devour its human body, and begin preying on human's. The Grani, a different alien life form implanted in Kotori Takatori, is said to be capable of instantly destroying all life on the planet when it hatches.
In chapter 110, the Drassil of Rurumi hatches. She experiences nausea, headaches, and excessive sweating prior to hatching. Immediately before she hatches her headache becomes so intense that it feels like her head is splitting in two, causing her to unintentionally scream. Upon hatching her Harnessed opens and an enormous creature forces its way out of her Harnessed. It then proceeds to devour its former host.