Despite her boyish looks, Otto is actually a girl and one of the last Numbers to be completed, along with Deed and Sette. Being a taciturn person makes hard for her to communicate with others. But due to their akin personalities, she and Deed share a strong bond that allows them a degree of silent mutual understanding. In the absence of any of her oldests sisters, Otto is the one who takes the leadership over the late generation Numbers. -Wikipedia-