Mio Nanami (七海 澪 Nanami Mio) was Touko's elder sister.
Seven years before the start of the series, while still at high school, she died in a traffic accident, which had a traumatic effect on Touko.
Appearance
Overall, Mio looked very similar to Touko. She had long black hair, as Touko does now. In the manga, Mio's face is usually obscured whenever photographs or flashbacks of her are shown.
Background
Mio was seven years older than her younger sister Touko. The pair were close, with the shy Touko often hiding behind her sister when meeting other people.
At high school, Mio was the president of the student council and had a glowing reputation as a model student, advanced in both academics and athletics. She was at the center of social life at the school, and both students and teachers depended on her.
However, seven years ago, Mio was killed in a traffic accident, just before the high school cultural festival. Her death also ended the student council tradition of putting on a play at the cultural festival. This event was traumatic and formative for Touko, who resolved to complete everything her sister had left unfinished.
Personality
Most people knew Mio as friendly, honest and hard-working, with a dedication to achieving her goals. This is how Touko saw her sister, and is the image that she attempts to emulate.
However, those who were close to Mio, like fellow student council member Tomoyuki Ichigaya, knew a different side to her. Far from being hardworking, she usually delegated student council tasks while only giving speeches and basking in attention and admiration. At one point, she even asked the other student council members to help her do her homework, which they all did willingly – even those who truly did know her still adored her.