Mirei Sakaki is a main character in the series Hitohira and serves as the president of the Drama Club. She has a serious personality and is able to forcefully command the other members of her club, often using a tough demeanor to get things done, including persuading her younger brother Kai to help with club activities. Despite her authoritative front, she is normally a balanced, courteous, and friendly young woman who is empathetic and willing to listen to others' problems.

Her backstory reveals that she first met Nono Ichinose a couple of years before the story begins, when she noticed Nono reading alone and brought her into the Drama Club. The two were close friends initially, but over time developed an ongoing rivalry. Mirei's feelings toward Nono are complex: she may have romantic feelings for her, as hinted by another character after Nono rejected someone else's offer to share an umbrella. Although Mirei does not show it openly, she worries about Nono's health problems. At one point, she tried to prevent Nono from using her voice as an actress by not allowing her to act in a play, but this effort failed.

Mirei's role in the story is that of a strong-willed leader who drives the Drama Club's activities and often clashes with Nono, who leads the rival Drama Research Society. This rivalry is a key dynamic, but underlying it is a mutual respect and concern. Mirei is also shown to be terrified when Nono is truly angered, indicating that Nono can unsettle her otherwise commanding presence.

Notably, Mirei is capable of forceful leadership but also demonstrates a caring side, particularly toward those she is close to. Her abilities lie in organization and direction, as she manages the club's affairs and steers its members toward their goals. Her development is subtle, as she learns to balance her protective instincts with allowing others to pursue their own paths, particularly concerning Nono's determination to act.