Episode 1

In Giha village, an underground town, Simon and Kamina live mundane lives with the constant threat of earthquakes. During an attempt to escape to the surface - something almost unheard of - Kamina and Simon bear witness to a monstrous Gunman, as it crashes through the ceiling into the middle of their subterranean home. Together with the Gunman's pursuer, a girl from the neighbouring village, Yoko, the two young men find the key - a small Gunman buried deep in the ground, named Lagann by Kamina - to both defeating the massive intruder and leaving Giha Village.

Story
Simon, a 14- year- old boy who lives in the underground village of Jeeha, is doing his job of digging to expand the village when he uncovers a small drill that glows at his touch. He leaves his hole and comes out to the village, where a few girls see him and mock him.

He walks away with his head down and bumps into Kamina, a person he calls Aniki or bro, even though they have no true relation. He grabs Simon and says he is heading to the surface. They ride some mole-pigs to try and break through the roof but are foiled by the village leader, who says Kamina is a liar about the surface, just like Kamina's father. Kamina claims he and his father went to the surface earlier, but no one believes him so he is thrown in jail, and Simon is sent back to dig more. While he is digging he finds another discovery, a face. He quickly rushed to break Kamina out of jail. He says he will take Kamina to the face he found, but the village leader finds them again. But before he can punish them, a gigantic robot breaks through the roof, and with it a girl.

They try to fight the Mecha but are no match to it, so Simon says he will bring them to the face and maybe it could help them. Simon brings Kamina and the girl to the face, and the drill over his neck starts glowing more, and he learns that it can activate it.

He activates the mini-mech, and confront the larger "Gunmen" as they are called. Kamina says that "Heaven may forgive you, but this Lagann will never" which gave the mini-gunmen the name Lagann. Using the drills on Lagann they defeat the enemy, and break through to the surface, and the girl tells them her name is Yoko.

The sight amazed Simon and Kamina but Kamina and Yoko soon learn they are falling. Simon closes the hatch but they crash into the ground,sending everyone out. Simon comically lands on Yoko's breasts, she responds with a smile, however Yoko's face suddenly widens with shock as she pulls him even closer to her breasts to reveal two more Gunmen behind them.

Major Events

 * Introduction of the main characters
 * Introduction of Gunmen

Trivia

 * The first Gunmen is never named.
 * At the beginning of the episode, right after the intro there is a clip of Simon and 2 unnamed people on the Cathedral Terra with the Gurren Brigade in the background.
 * It was later said by the writers that the begginning shows what were to happen if Simon had ignored the Anti-Spiral's final words and the event at the start was Simon about to cause a Spiral Nemisis. As it turned out,this answer came from a theroy presented by fans to the creators.