After the attack of the Blight, a small number of legionnaires was trapped in the collapsing warp portals than send them ouside the know galaxy. They traveled in time and space to the far away lost galaxy. When they awoke the legionnaires discovered than the lost galaxy, also known as the kwai galaxy and second galaxy, it was the dominion of the mysterious Progenitor who was the creator of the several intelligent species than lived in the second galaxy, but also he was bored of his creations and choose to erase them using the merciless Progeny. The Legion, searching for a way to return to their home, would go against the Progenitor only to discover him as one of their members.
After returning home with the help of the Kwai Shikari, the Legion wold return to the lost galaxy to help their inhabitants to rebuilt their lives free from the Progenitor.