The Spiral Nemesis is a mysterious phenomenon said to occur due to the excessive evolution of Spiral Energy and the unseen overarching antagonist of Tengen Toppa Gurren Lagann.
Long ago, a Spiral race discovered the possibility that the evolution of Spiral Power would lead to the creation of a force known as the Spiral Nemesis and bring about the destruction of the universe. To prevent such an event from occurring, the race sealed away their Spiral power, with their collective unconsciousness taking shape as the Anti-Spiral, and waging war against all other Spiral races to cull their numbers to the point where they would be unable to evolve and generate enough Spiral power to form the Spiral Nemesis.
The exact of the Spiral Nemesis, or even if it is actually real and not just a myth, is unknown. The only glimpse of a possible Spiral Nemesis is seen at the beginning of the first episode of Tengen Toppa Gurren Lagann, which shows an alternate version of Simon possibly bringing about the Spiral Nemesis.