Esmeralda (エスメラルダ Esumeraruda?) is Masako Natsume's penguin partner. It is the only one of the currently known penguins to have a name. Esmeralda aids Masako in her antics, for example, we see her sharpening a scalpel knife that is to be used to threaten Shoma. Esmeralda is introduced in to the show along with Masako but no details about the penguin are revealed whereas details of Masako's life are. For example, we do not know how Masako recieved this penguin or why it is different in appearance to the other penguins, but this is of no concern and details such as these would surely not enrich the plot.
Esmeralda is slightly taller and more slender than Penguins 1, 2, and 3. Also, her coat is black and its design creates a white, heart shaped face. She has two tufts of fur on either side of her head.
It has been commented that the penguins in the show are reflections of the characters that they are associated with, and this is apparent in the series as the penguins are often seen acting out the same scenes as their 'owners' or doing things associated with them. So, Esmeralda shows constant signs of affection towards Kanba
Takakura's penguin, making romantic advances on him, just like her 'owner', Masako, does with Kanba.