Miri Yanagiba is a 15-year-old student at Higashizaka High School who avoids attending classes. She sports mid-back length dark purple hair, typically styled in twintails, with bangs framing her face. Her purple eyes and a distinctive beauty mark beneath her left eye are notable features. Regardless of the season, Miri always wears winter clothing, especially a scarf, to prevent colds due to her fragile health. This habit originates from her first day of school when, without a scarf, she caught a cold that escalated into pneumonia. Missing those crucial initial weeks for forming friendships led to her feeling isolated and choosing not to return.

Generally friendly, Miri is particularly drawn to eccentric behavior, though she often appears sickly or reserved. She struggles to integrate socially, initially avoiding classmates like Rui Nagata when introduced by Daisuke Higashida. However, she warms up to those she finds intriguing, such as when she befriended Rui after observing Rui's misunderstanding involving Daisuke's pet raccoon and another character.

Miri shares a close bond with Daisuke Higashida, whom she affectionately calls "Higashi." He actively encourages her social development, prompting her to interact with others like Rui. Through these efforts, Miri forms a friendship with Rui, partly connected by their mutual interest in Daisuke. Her background includes a familial link to the Wagnaria restaurant; she is the granddaughter of an elderly customer only visible to employee Sayuri Muranushi, establishing her indirect connection to the restaurant.

Her development focuses on overcoming self-imposed isolation. Starting the series avoiding school entirely, her growing friendships with Daisuke and Rui contribute to a gradual reintegration into social settings. Her increasing presence at Wagnaria and interactions with classmates suggest movement beyond her initial social anxieties.