Menchi

Episodes 10 and 19 in particular are focused almost exclusively on Menchi, both episodes being modeled after children's stories about talking or otherwise extraordinary animals. The earliest record of Menchi is a flashback in the anime, showing her previous owner - a kindhearted old man who may or may not have taken care of her in lieu of younger owners. Throughout episode 10, Menchi has frequent flashbacks of her previous owner, and longs to find him and be happy once more. Through these flashbacks, it is shown that the old man set Menchi free because he was worried about his own limited time on this earth... it's not until later, however, that she abandons this hope after the old man betrays Menchi and her canine companions, reluctantly returning to Excel and Hyatt at the end of the episode. Her reason in doing so is debated, however, as she continues to makes numerous escape attempts throughout the rest of the series.

Menchi also sings the ending credits theme at the end of each episode in the anime, bar the final episode, in which her role is reversed with that of the girl who translates Menchi's dog lyrics in the previous closing sequences.

"[Menchi's] breed, though not stated in the anime or manga, appears to be a small Shiba Inu, a baby Akita Inu, or a Hokkaido." (Wikipedia)