The Stigma is a army of cyborgs and robots in Hikari ochiru II. They are led by one of the villains of the second series, who has one motive: to dominate the galaxy. The Stigma serve as the main antagonists in the fifth series, almost replacing Chi and Kyozetsu, although unlike Chi and Kyozetsu, the Stigma had everything laid out in advance so that they could both protect vital operations and attack enemy worlds at the same time.
The Stigma's origins are as mysterious as their motives. They have traversed the galaxy, taking over various world's and if they're not satisfied with that world they leave the world dead or dying in their wake. Among their victims is Nariko's home world, along with everybody on her world except Nariko herself who escaped to find Andre and his friends as ordered by her mother. Nariko's mom told her to go to find Andre due to her believing Andre was the one Ryoku foretold.