Living underground in Giha Village, Simon and Kamina dream of a life on the surface. When their home is invaded from above, it is up to them to activate the mysterious mecha Lagann and save their village.

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.

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.