Chio Miyamo, a first-year student at Samejima Private Academy, lives by a self-imposed creed to "appear below average," deliberately avoiding academic and social prominence despite significant physical capabilities. An avid fan of Western video games—especially violent shooters and stealth titles—she operates online as "Bloody Butterfly" and openly disparages Japanese games. This gaming passion frequently spills into her daily life, leading her to apply video game logic and techniques, like parkour moves inspired by stealth games, to routine obstacles such as her commute. These attempts often escalate into exaggerated, perilous situations. Though her athleticism enables sporadic success, she frequently exhausts herself in the process.

Her daily commute unfolds as a series of unpredictable misadventures: scaling rooftops to bypass construction, encountering delinquent biker gangs, or contending with sudden urges like desperately needing a bathroom—once resulting in her accidentally entering a men's restroom. A pivotal early incident involves her accidentally elbowing motorcycle gang leader Mayuta Andō off his bike. To intimidate him, she adopts her "Bloody Butterfly" persona, fabricating an underground reputation that inadvertently convinces him to quit gang life and seek legitimate work. This encounter establishes a dynamic where Andō develops romantic feelings, frequently attempting elaborate methods to impress her—including acting out scenes from BL games under the mistaken belief she enjoys such content. Chio initially misreads his intentions as possibly gay, but their interactions eventually lead to mutual romantic feelings. Andō clearly confesses in chapter 43, and they begin an official relationship.

Her closest friend is Manana Nonomura, her companion since elementary school. Despite their bond, their relationship features mutual backstabbing and occasional betrayal, with Manana often participating in or enabling Chio's schemes. Chio also navigates relationships with classmates: Yuki Hosokawa, a sports ace and exhibitionist raised by nudist parents; Momo Shinozuka, a socially awkward public morals committee member; and Madoka Kushitori, Kabaddi Club captain whose recruitment efforts pull Chio into unexpected athletic confrontations. Chio approaches social challenges with pragmatism and gaming-inspired logic, sometimes resulting in shared antics like group decisions to forgo underwear during commutes. She improvises solutions, such as fabricating a make-out session with Manana to avoid detection while spying on Yuki.