Nebula is the main setting of Thunder Force II.

Details

Nebula was originally a protectorate of the Galactic Federation, but ended taken over by the ORN Empire forces, which used the planet to house their battle fortress Plealos. The homeworld of Reid A. Jupiter, Nebula is actually a hollow planet with six layers of space inside of it, with the population living on underground cities. After the destruction of Plealos, the planet is freed from the influence of the ORN Empire.

Trivia

• In actual astronomical terminology, a nebula is a large, interstellar cloud of dust and gas where stars are formed.