Karen Minamino, a clone engineered by a shadowy organization, first surfaces under observation at an orphanage while disguised as an ordinary child. Debuting as a quiet, enigmatic seventeen-year-old, she possesses long dark blue hair, yellow eyes, and limited facial expressions, speaking only when essential. Her attire—a short-sleeved purple buttoned shirt and matching short skirt—features pink underwear, distinguishing her from others in the series. A purple butterfly insignia on her left breast harbors micro-encoded data that decrypts to the phrase "the gate of the truth will be opened by the sleeping butterfly" alongside map coordinates, guiding the group to an underwater base and propelling the central plot.

Afflicted by amnesia, fragmented memories gradually return during the journey. Exploration of a sealed laboratory at the underwater site confirms her identity as one of many genetically engineered clones designed for high intelligence and perpetual youth, explaining her absent history and the organization’s pursuit.

Subsequent appearances show drastic physical changes: she shortens her hair and employs disguises like fake glasses. Working at a maid café, she wears a catgirl maid costume among other outfits and declares herself "eternally 17 years old" during age discussions. Her habit of measuring others’ bodies or examining clothing, initially misconstrued as potential lesbian interest, is later revealed as tactical reconnaissance for missions or disguise procurement. She investigates mysteries alongside allies, retaining her reserved nature while displaying loyalty to the core group.

Her role evolves to include combat and strategic operations, where she applies her intellect and clone background against antagonists. Across media, her development consistently underscores her clone origins, agelessness, and steady integration into team dynamics despite emotional restraint.