Aim for the Top! NEXT GENERATION ~Excavation Battleship Alexion~

Hundreds of years after the top forces left for the center of the galaxy, the Earth Army, whose science and technology has declined, and the Sirius Army, who have built a spiritual energy civilization with the descendants of immigrants, continue to fight between humans. Takeshi Sawamura, whose father is a refugee from Sirius, meets two beautiful girls in the S-TOP unit on Earth, but their true identities are space monsters... a sequel to Gainax's OVA "Aim for the Top!

The prologue was published in Comic Gunbuster.