Miina Miyafuji is one of the main heroines in Please Twins!. She is a sixteen-year-old high school girl with short pink hair and unusual blue or purple eyes. At the start of the story, Miina arrives at the home of Maiku Kamishiro carrying a childhood photograph that shows a boy and a girl. Based on this picture, she believes she might be Maiku's twin sister, and that belief sets the central mystery of the series in motion.

Miina has a hyperactive and outgoing personality. She is energetic, spunky, and often presents herself as happy-go-lucky. This bright exterior, however, masks deeper insecurities and aspects of her past that she does not readily share. She is capable of handling household tasks such as cooking and cleaning, and she actively contributes to the household when the three main characters begin living together. Her motivations are driven by a desire to uncover the truth about her family background while also navigating her growing romantic feelings for Maiku. She is afraid to act on those feelings because she fears that acknowledging them would be inappropriate if she is indeed his sister.

In the story, Miina forms a key relationship with both Maiku and the other female lead, Karen Onodera. She and Karen initially present themselves as potential twin sisters to Maiku, and they develop a friendly rivalry. Together they create a "Love Alliance" to manage their shared feelings for Maiku. Miina's relationship with Maiku deepens over the course of the series, though her internal conflict about their possible sibling bond complicates her actions.

Miina undergoes noticeable development as the story progresses. Her cheerful facade cracks when her past is brought to light, and she is forced to confront painful memories. When Karen discovers through a diary that Miina is not Maiku's biological sister, Miina runs away, overwhelmed by the implications. She eventually returns, and at a train station she reunites with Maiku, confessing her love for him. It is ultimately revealed that Miina is the girl in the childhood photograph, but she was a childhood friend rather than a blood relative. This resolution allows her to pursue a romantic relationship with Maiku without the stigma of incest.

Miina does not possess any supernatural or extraordinary abilities. Her notable traits are her energetic spirit, her domestic competence, and her capacity to hide her true feelings behind a lively demeanor. Her role in the story is essential to the love triangle and to the mystery of which girl is Maiku's twin. Her emotional journey from uncertainty to self-acceptance and love forms a central thread of the narrative.