Aya Mitsuki is the central protagonist of the story. She is a first-year student at the prestigious Kuromi Girls Academy, an elite boarding school dedicated to cultivating perfect, elegant young ladies where video games are strictly forbidden. Unlike many of her wealthy peers, Aya comes from a modest background and attends the academy on a scholarship, a fact that fuels her determination to succeed and fit in. Her primary goal is to be counted among the school's best students, known as the Black Lily, and to transform herself into a refined young lady.

In her public life, Aya is known for being outgoing and cautious, diligently working to project an aura of elegance that masks her true, more eccentric self. However, this carefully constructed facade hides a past life. Before entering Kuromi Academy, Aya was a passionate and highly skilled fighting game enthusiast who had spent years playing, often beating the boys in her neighborhood. She eventually decided to leave this hobby behind, viewing it as an obstacle to becoming the person she aspired to be, and enrolled in the academy to start anew.

Her resolve is tested when she accidentally discovers that Mio Yorue, the school's most popular and seemingly perfect student known as Shirayuri-sama (White Lily), is secretly a hardcore, trash-talking fighting game fanatic. Mio quickly deduces Aya's own gaming past from the calluses on her hands, and despite Aya's attempts to deny it, she is pulled back into the world she tried to leave behind. This discovery forms the core of the story, as their shared secret and mutual love for fighting games forge an unexpected and intense bond. Aya finds her motivations shifting as her dormant passion for competition is reignited, and she becomes deeply involved in Mio's world, leading them to secretly enter major fighting game tournaments.

Regarding her key relationships, her dynamic with Mio Shirayuri is the most significant. She deeply admires Mio's mysterious desire to win and finds herself nervously shy in her presence. Their relationship is a complex mixture of rivalry, partnership, and deep affection that blurs the lines between friendship and something more. She also shares a close bond with her roommate, Natsume Sakizaka, who often misinterprets the intensity of Aya's relationship with Mio and supports them in their endeavors.

Over the course of the narrative, Aya undergoes significant personal development. Initially conflicted about her two identities, she gradually learns to reconcile her past as a gamer with her aspirations of being a young lady. Her journey is not just about winning matches but also about self-acceptance and understanding that personal passions do not have to be abandoned in the pursuit of one's goals. Later story developments see her facing emotional challenges, such as confronting the possibility that her intense rivalry with Mio might be evolving in a way that leaves her behind, testing the foundation of their relationship.

In terms of notable abilities, Aya is a formidable fighting game player. Her skills, honed from childhood, include a deep understanding of game mechanics such as frame data and combos, as well as a strategic and analytical mind that allows her to outthink her opponents. In the live-action adaptation, her main character of choice is Cammy White. Her gaming proficiency is depicted as being on par with, or at least complementary to, Mio's raw talent and aggressive style.