Crystal is a rare mechanism that mysteriously generates on a persons body for no apparent reason; the chance that a Crystal generates is only one in ten thousand and, should a person grow a Crystal, the person becomes a Drive-Union. After the Wadatsumi Mass Vanish Incident, the amount of Unions increased tenfold. Union's who existed before the Wadatsumi Incident are collectively known as Irregular Types, who act differently to more recent Unions; there is little information on them. Unfortunately, those who become Unions will usually die, due to the mental instability causing them to commit suicide, or their Crystal reaching Phase 6 – one Union has survived infection, however, but this was because of unique circumstances surrounding his progression through the Phases.