The little sister that Santa brought to Haruma. She is sweet and very innocent, all her knowledge of the world initially derived from an instruction manual she was given before her delivery to Haruma's home. Apparently the manual does not cover all situations and it is not really written for someone of Choco's level of experience. Some of the information is even quite inappropriate for someone of her age... Choco appears to be a sweet girl and is very fond of her new "onii-chan", as she immediately identified Haruma.

Source: wikipedia