Mirai Onozawa is the big sister of Yuuki. Mirai's name means "future" in Japanese.
It may seem like she doesn't like him and that she thinks he's annoying but she actually really loves him. As seen in several episodes she really does love her younger brother. When her and Yuuki were separated she was kind of frantic and worried about her brother. During the last episodes she was so shocked that her brother died she imagined that he was still alive. Overall Mirai is nice person and loves her brother but can be slightly irritable at times and can have a hard time accepting strangers for example Mari.
Mirai has black eyes and short brown hair. Her attire consists of a green shirt with a button up jacket, a blue skirt with a light blue star, a pink satchel purse and red open toed shoes. Her school uniform is like any other. Its a white shirt with a blue collar that has two white stripes on it, a red bow, a knee length blue skirt, brown shoes, and short black socks.
Mirai was not so quick to accept Mari but eventually she did. Mari is the one who helps her look for Yuuki when they got separated after the earthquake occurred. Mirai, Mari, and Yuuki all meet each other several times before the earthquake actually happened and it also appeared that Mari was meant to look out for her and her brother.