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.

During the following seven years, a new civilization rises and prospers under Simon's leadership. However, these peaceful times come to end when the threat mentioned in Lordgenome's last words starts to reveal itself.

At last, Simon and Nia are reunited, and by combining the power of its members, Team Dai-Gurren creates the galaxy-sized Tengen Toppa Gurren-Lagann, and engage the Anti-Spiral threat in a decisive battle to determine the fate of the universe.