DIA51 is the main villain and final boss of Aleste.
DIA51 is a man-made supercomputer created for environmental control, which among other things created new plants through genetic engineering for the purpose of oxygen synthesis. One day a sudden earthquake struct, it's vibration causing DIA51's data to deviate. It was soon noticed that DIA51's operations were going haywire, as the surface temperature started to raise and all communication with the base were DIA51 was located was interrupted.
The government immediately decides to take action, but discovers that DIA51 was overgrowing and mutating plants, which become parasites and start to both cover the cities and infect humans, who are turned into mindless slaves. It was later revealed that the earthquake which caused DIA51 to go haywire was caused by one of the seeds planted by the Vegant.