In a dark void known as the Lightless Realm, a group of children meet and bond, but are then separated and returned to their own dimension. Years later, these children reunite to fight Admonitions, monsters that originate from the same void, using robots known as Vess. However, their efforts only slow the ever-encroaching and expanding Lightless Realm from infecting their world. Their lives take a drastic turn when a new foe appears in the form of a Corpse, whose song is rumored to kill any who hear it within nine days. The Corpse Song is heard by the group, and with this, they each begin to pull away and become caught up in their own personal problems—ultimately threatening the fate of humanity.

Lamune tells the story of a boy named Kenji and his childhood friend Nanami. Although, everyone seems to know that they have a relationship, neither are determined to push it anymore than close friends. The story goes through flashbacks, explaining why they are such close friends and any action doesn't seem to push them apart, but draw them closer. (Source: ANN)

On the dusty streets of the castle town Dayah in the Fortna Kingdom, a young orphan named Nina steals for survival. Experiencing one tragedy after another, she has little to hope for in her life. Believing it best for Nina, her closest friend, Saji, hands her over to Second Prince Azure Seth Fortna, who has been searching for someone with unique and intense deep-blue eyes—just like Nina's. The kingdom's princess, the revered Astral Priestess Alisha, has recently died on her way to the Galgada Kingdom, where she was to marry the tyrant First Prince Sett. However, her death is concealed for political reasons, and that is where Nina needs to step in. With nowhere else to go and no one to turn to, Nina assumes Alisha's identity and future duties. But with each moment spent with Azure, Nina feels herself drawn to his warmth, fearing that once she is wed to another, nobody will remain to remember her true self.

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?