The Mirial system existed within the Outer Rim and was a star system. Within this system was the planet Mirial, the homeworld of the Mirialan species, who are near-human. At least one additional planet also resided in the system. Its location was designated as Q-4 on the Standard Galactic Grid.
Prior to 1 BBY, a small rebellious militia originating from planets of the Mirial system was active, but its members were subsequently imprisoned by the Galactic Empire in various prisons to isolate them. Despite these measures, the Mirialan Yalla, a member of the militia incarcerated at Imperial Detention Center & Labor Camp LEG-817 on Wobani, successfully established contact with fellow prisoners from the same group at Wobani, exchanging brief coded messages. Sometime after this, the group's attempt to break out of the prison failed, resulting in Yalla's death.
The Mirial system's introduction to the new Star Wars canon occurred via a galactic map included with Star Wars: The Force Awakens Beginner Game. This roleplaying game was produced by Fantasy Flight Games and launched in 2016. The system's name was later specified in the 2017 young-adult novel Rebel Rising by Beth Revis. Within the Star Wars Legends continuity, the Mirial system received its initial, though indirect, mention in the 2001 novel Cloak of Deception by James Luceno. Its identification followed in the 2009 reference book The Essential Atlas, authored by Daniel Wallace and Jason Fry.