This page may contain story spoilers for the entire Phantasy Star series. If you have not played some of the series and do not want plot details revealed, please do not continue.
Far from Earth, the Algo Star System can be found in the Andromeda galaxy. This solar system consists of one fixed star called Algo, four planets, and a number of artificial satellites. Most of the classic Phantasy Star series takes place in this system. Of those games, only Phantasy Star III and Phantasy Star Gaiden are set elsewhere. Even so, Phantasy Star III references the system with a flashback.
The four planets are Palma, Motavia, Dezoris, and Rykros. The artificial satellites vary at different points in the system's history. Gaila, Kuran, and Zelan are among their numbers. Lashiec's Air Castle was also an artificial satellite for a brief time.
This star system was artificially created as a seal for a dimensional portal. This seal weakens once every thousand years, allowing one Dark Force to appear. The ultimate goal of each Dark Force is to break this seal, which requires destroying the planets. Once Palma was destroyed, the seal became considerably weaker, eventually failing completely at the next thousand year interval.
Only the star, Palma, Motavia, and Dezoris make up the dimensional seal. Rykros is actually an additional planet, meant to serve as a warning system to be revealed when the seal is about to fail. The existence of Rykros was not known until shortly before the seal failed.
There are three major civilizations in the system: Palmans, Motavians, and Dezorians, with each being native to the planets they are named after. Palmans, as the most technologically advanced, claimed rulership over all three planets after developing space travel. Palmans became the dominant lifeform on Motavia, but did not extensively settle on Dezoris. After Palma's destruction, the Palman government fell, leaving no central government for the system or either remaining planet.