The story takes place between the first and second season, where Rimuru confronts the swirling conspiracies in the Coleus kingdom.

Kim is living a peaceful life with his father as a farmer on their planet until one day when a runaway spaceship is detected moving at a high speed towards his father's farm. To rescue his father Kim jumps on board the ship and manages to land it safely before it crashes. On board the ship he finds a severely Injured lone survivor whom with his dying words begs Kim to take something of his to the Galactic Fleet. He then transfers something that was attached to his arm onto Kim's arm. The thing was a Lens and its transferring should have been impossible and having it has turned Kim into a Lensman. Other than giving Kim unknown powers it also contains vital information for the victory of the Galactic Fleet over the evil Boskone Empire. Kim must now using the spaceship Britannia bring the Lense to the Galactic Fleet. But this is not an easy task when Lord Helmet of the Boskone Empire is willing to use everything in his power to stop him.

After battle in first season battleship Amanohara was serious damaged and need to repair. It land on island where a Gogyou festival just begin. Umakai Shintaro and his five girls student who know as Raimu Unit begin enjoy a peace time in that island. But the enemy still follow them around. How Umakai Shintaro and his five girls student fight against the enemy. Still his five girls student begin try to draw his attention into them.

Rikotto, Zuzu, and Paroru are intelligent furry creatures who believe more than anything that the world outside their island is too dangerous to explore. Despite this, Rikotto and Zuzu long to see the world that produces the mysterious objects that wash up on their shores. After a particularly exciting find, Rikotto convinces Zuzu to build a boat, and they set sail across the sea with their reluctant friend Paroru in tow. At first, the trio finds the foreign land beautiful and exciting, but they are overwhelmed when they come across a bustling city of humans. When Rikotto and Zuzu get captured by a circus ringleader who intends to put them on display, Paroru has to decide what fears he is willing to face for his friends.