Kamina and Simon must work together to defeat a dangerous new Beastman threat.

Team Dai-Gurren managed to take control of the enemy fortress, but is still mourning the death of one of their own, especially Simon. After falling off a cliff, he notices a Gunman throw a capsule into a deep valley. Simon inspects it and finds he is able to open it with the same drill key he uses to pilot Lagann, and inside is a young human girl named Nia, but their introduction is cut short when an enemy Gunman appears.

The last of the Divine Generals fall, and the city of Teppelin collapses, revealing a Gunman of gigantic proportions. Simon and Nia struggle to pass through it in order to confront her father, the Spiral King himself.

After the Anti-Spirals' first attack and Nia's astonishing announcement, Simon looks desperately for her, while Rossiu finally completes his secret project.

To soothe the public opinion, Rossiu overthrows Simon and puts him under arrest. But when the Anti-Spirals launch a large-scale attack on Kamina City, he is left with no option but to let Simon engage the enemy using the Gurren-Lagann, not before resorting to extremes to put him under his control.

After finally transforming their flagship into the Super Galactic Gurren-Lagann, Simon and his friends successfully fight back against the enemy. When their enemy starts to use their own memories and desires against them, Kamina reappears to help.