Boota

The unofficial mascot of Team Dai-Gurren, Boota (ブータ, Būta) is a small mole-pig from Jeeha village, who Simon keeps as a pet. Boota is characterised by his sunglasses and star pattern surrounding the tail in his rear end. No matter how many years pass, Boota's physical appearance does not change. Although he can't talk, he can understand humans, and even has seemingly near-human intelligence. His favorite spots to stay are between Yoko's breasts or on Simon's shoulders. He has ripped off his tail and consequently the tip of his rear end as an emergency food supply for Kamina and Simon so as to provide energy to the starving duo during a crucial fight scene, and also has served as a morale figure to Yoko, when she first hesitated at piloting Gurren in place of Kamina. Interestingly enough, he too was thrown in prison along with Simon, and even had his own pair of miniature handcuffs. When Simon and Viral broke out of jail, Boota loyally ran to Simon's shoulder. However, upon seeing Yoko again, he hastily jumped in her cleavage once more.

Boota proved his true value to Team Dai-Gurren in episode 25, when he asked Viral to enter into Gurren's cockpit and from there, released a massive surge of Spiral Energy to aid a worn-out Simon in his task to power up Chouginga Dai-Gurren. Lordgenome stated that this occurred not only because humans aren't the only beings capable of generating Spiral Energy, but it also may be a reaction from Boota, being frequently exposed to Simon's Spiral Energy. In episode 26, Boota stands to protect Lordgenome from the Anti-Spiral trying to attack him, and when their Spiral Energy resonates, he is transformed into a humanoid, resembling one of the characters at the beginning of the first episode. This, however, would turn out to be but a mere illusion set up by the Anti-Spiral, as Boota already had Spiral Energy, and it was his dream to be able to fight alongside his friends, rather than be just a pet. Curiously, his human form seems to appear in the prologue of the first episode.

In the epilogue, he is seen wandering the world alongside an aged Simon.

Source: Wikipedia