Karen Ayanokouji is a second-year student sharing Jun'ichi Nagase's class. Hailing from considerable wealth, she prides herself on embodying the refined manners of a proper young lady. Her appearance includes blond hair styled in ringlets with v-shaped bangs, a distinct ahoge, and decorative hair beads. She possesses striking blue tsurime eyes and a pale, slender frame, standing 160 cm tall with measurements of 84-56-82 cm. Karen typically wears her school uniform accessorized with ribbons and thigh-high stockings.

Her personality embodies the "himedere" archetype, marked by arrogance, pride, and pronounced self-assurance rooted in her affluent upbringing. Over time, she forges a close bond with fellow high-society student Yuuhi Katagiri. Despite her initially haughty demeanor, Karen experiences authentic romantic development, culminating in a confession of her feelings for Jun'ichi Nagase. She functions as a supporting character, enriching the central narrative through her interactions primarily with Yuuhi and Jun'ichi.