Tengen Toppa Gurren-Lagann S01E03 - Who Do You Think You Are, Having Two Faces!!

In the aftermath of the previous battle, Kamina, Simon, and Yoko proceed to forage for provisions. However, a chance encounter with a formidable Beastman, Viral, and his powerful Gunman forces the Gurren and the Lagann to combine to form a new Gunman.