Sumie Ayado is an otaku girl burdened by significant social difficulties. Childhood experiences of peer rejection and ridicule, triggered by openly sharing her anime and manga passions, caused her to retreat into isolation. Though her parents were supportive, school bullying instilled deep-seated low self-esteem, leaving her convinced she is unattractive and unworthy of friendship or romance.

Physically, she has brown hair, grey eyes, and wears glasses. She is typically seen in her school uniform: a blue skirt, white shirt, and green bow. Her personality blends kindness and empathy with pronounced social awkwardness, sensitivity, and a tendency to cry easily. Past bullying makes interpersonal interactions challenging, leading her to often avoid them.

A pivotal moment occurs when she accidentally bumps into Hikari Tsutsui. Their connection over shared otaku interests sparks her romantic feelings for him. However, her admiration remains largely unrequited due to his relationship with Iroha Igarashi, whom Sumie idolizes as the "perfect 3D Girl." After Hikari rejects her, Yuto Ito—Hikari's best friend and fellow otaku—consistently supports her, eventually leading to a romantic relationship between Sumie and Yuto.

Her development includes a significant post-high school trajectory. Following a separation from Yuto, she marries another man but later divorces. The series concludes with Yuto, learning of her divorce, inviting her to dinner, hinting at a potential rekindling of their relationship.