Natsumi Hirakawa

She is a short, sporty and athletic girl who can beat anyone at sports. Although she generally does not have desires, when she finds a goal, she is able to single-mindely pursue it. Although she is generally a calm person, she has nyctophobia. She is very innocent, often being stopped by her friends from undressing in public in front of boys. She is a tomboy and refers to herself in a very masculine way as she uses the male-singular pronoun "boku" to refer to herself and always dresses in boys clothing except during the epilogue of the anime. Her number on the class list is 17.

(Source: Wikipedia)