Universal Century 0136, shortly after Mobile Suit Crossbone Gundam - Skull Heart.

Bernadette Briett's step-mother Europa Dogatie, flees to Earth to warn the Crossbone Vanguard that the Jupiter Empire is building a giant colony laser in order to destroy Earth. Tobia must race against time and agents of the Empire to recover a means with which to get to Jupiter, and to recruit the best pilots he can muster for what seems to be a suicide mission.

This is loosely inspired by Akira Kurosawa's Seven Samurai film.