Maruo is one of Maruko's classmates and serves as the male class president and always wants to be admired by others. He has very thick glasses because he is a very serious student and studies very hard every day; black lines appear on his face nearly all of the time, especially when he seems euphoric. He is paranoid that his classmates are seeking to replace him as male class president and will target classmates that stand out and do well to discourage them from running against him. His birthday is December 31, thus giving rise to his name.