Miki is the younger sister of Tooji, a former captain of Sohoku's bicycle club and the current manager of their family's bicycle shop. Though not much of their relationship is shown, they seem to get along very well.
Miki is a childhood friend of Imaizumi's. When they first met, she instantly shares with him that she adores bicycles. Though Imaizumi is sometimes frustrated by Miki's actions, such as when she invites spectators to his first race against Onoda, they have maintained a friendship throughout the years. Presently, Miki is pleased about the positive changes she has seen in Imaizumi's personality since he has joined the bicycle club.
Aya is the best friend of Miki. She is a member of the tennis club at Sohoku High. Though Aya doesn't have much interest in cycling, the two get along quite well. Miki calls her "Aya-chan."
Miki has been very friendly towards Onoda starting from their first meeting, which makes Onoda think that even people from sports clubs can be nice. She even does research to find out about him because she was curious about his cycling. She often talks to him during school, which Onoda is both embarrassed about and appreciative of. Miki is the one who corrects Onoda's saddle position during his first race with Imaizumi, as well as supplies him with a road racer later on. She constantly cheers Onoda on during races and is amazed at his rapid progression as a cyclist. While Onoda continues to be easily flustered around her, the two can certainly be considered friends.
Although Miki is generally regarded as behaving kind and motherly to her team members, she hit Naruko once after he pointed out that her breasts "grew" after summer break. Since this is the only act of violence Miki has displayed, it seems that she did not appreciate Naruko's remark, although, in actuality, he honestly believed he was giving her a compliment.