Ginga Eiyuu Densetsu: Arata Naru Tatakai no Overture

Led by Reinhard von Müsel, the Galactic Empire crushes the Free Planets Alliance in the Fourth Battle of Tiamat. Arriving in the Imperial capital of Odin to a hero's welcome, Reinhard's victory earns him a promotion to High Admiral and the distinguished title of Count von Lohengramm. On the other side, Yang Wen-li safely returns to the Alliance capital of Heinessen without fanfare and reunites with his dear friends.

Reinhard and Yang look forward to a long-awaited reprieve. However, at the request of the scheming Duke Otho von Braunschweig, the Imperial High Command orders the new High Admiral to invade the Alliance with a fleet of twenty thousand ships. After the Duke leaks the plan to the Alliance government, three fleets totalling forty thousand ships are sent to counter the incoming attack and recreate the famous Battle of Dagon. But even though Reinhard is outnumbered two to one, he has an ingenious plan—and Yang sees right through it. Will Yang's superiors heed his warning before it is too late?

(Source: MAL Rewrite)