C子

C-ko Kotobuki is A-ko's best friend and has depended on her since they met in kindergarten. Though the same age as the other two girls, C-ko is less mature. In the Japanese original, she frequently refers to herself in the third person. Though normally extremely cheerful, C-ko cries easily when facing hardship. She enjoys cooking, but the results are inedible. In the first installment of the series, C-ko is revealed to be the Fourth Princess of the Fifth Queen of the Lepton Kingdom of Alpha Cygni, an all-female race of extraterrestrials. She crash-landed on Earth when she was an infant, and the Lepton Kingdom has been searching for her ever since. However, C-ko is uninterested in her unearthly ancestry and wants to remain on Earth with A-ko.
(http://en.wikipedia.org/wiki/Project_A-ko)