Coal

Coal is a brown male capybara with dark brown stubby paws. His Jewel Eyes are made of dark purple coal and he wears a necklace made of black and white beads resembling prayer beads.

In Jewelpet Kira Deco, he is a member of Decoranain and the show's most active antagonist. He answers directly to the Dark General, a man he considers his father. On his mission to get the Deco Stones and corrupt them with darkness, he enlists the help of Opal and Io, who hate Ruby and her friends. Although he loves to boast that darkness is his only mistress, his continuous failures and humiliations eventually catch up to him.

In Jewelpet Happiness, he forms a Magic Gem.

He's a background character in the other seasons.

(Source: Jewelpet Wikia)