Youko Ryuuzaki is a wealthy student from an elite family attending Seika Girls Academy, recognizable by her glasses. She belongs to the school's Detective Club alongside four other affluent girls, habitually arriving in a chauffeured limousine. Her primary skill is mastery of disguise, allowing her to transform seamlessly into individuals of any age, gender, or nationality with high fidelity, coupled with precise vocal mimicry to replicate any voice from memory alone. She deploys these talents operationally during the group's confrontations with mercenary attackers targeting them at school, participating in tactical maneuvers like deceiving protective police guards and engaging directly in defensive actions. Her lineage includes unconventional aspects described as an "incomprehensible backstory" relative to the others, with one source identifying her as a descendant of Adolf Hitler.