Kyoka Jiro, alias Earphone Jack, stands out with her petite frame, fair skin, and slender build. Her dark purple hair forms a chin-length asymmetrical bob featuring two sound wave-shaped reflections framing her face. Triangular onyx eyes with long lower lashes and small eyebrows lend her a sharp gaze. Flexible plug-like appendages extend from her earlobes as her Earphone Jack quirk, functioning as prehensile limbs that stretch several meters. After the Final War, All For One destroyed her left ear and jack, replaced by a flesh-colored prosthetic with a pink tip. Her hero costume transitioned from stereo boots, a black leather jacket, and salmon shirt to a post-war design with silver-purple headphones, a sleeveless black jacket, and forearm Amplifier Jacks. Her personality blends pragmatic bluntness with hidden sensitivity. She often displays an unenthusiastic, teasing manner, particularly toward Denki Kaminari, using her jacks to poke or whack irritants. Beneath a sarcastic exterior lies fierce loyalty and protectiveness toward friends like Momo Yaoyorozu, alongside vulnerability about self-image and interests. She avoids horror themes and nudity despite her calm disposition. Initially embarrassed by her rock music passion as unrelated to heroism, she gradually embraced it as core to her identity. Born in Shizuoka to musicians Kyotoku and Mika Jiro, she inherited her mother's quirk. Though expected to pursue music, she chose heroism—a decision her parents supported by suggesting sound integration into hero work. This fueled early conflict between artistic and heroic ambitions at U.A. High. Her quirk enables versatile sound manipulation. The jacks detect faint vibrations and sounds within 12 meters for reconnaissance. Plugged into surfaces or equipment like stereo boots or forearm amplifiers, she channels her heartbeat to generate destructive vibrations or defensive waves. Key techniques include Heartbeat Distortion (shattering terrain), Heartbeat Surround (short-range sonic attacks), and Counter-Balance (nullifying sound assaults). Ranked 7th in Class 1-A's midterms, she applied strategic intellect in battles—coordinating with Kaminari to electrocute villains at U.S.J. or exploiting Present Mic's insect phobia during exams. Internships with Death Arms and Gang Orca honed her search and combat coordination. Development unfolded through key arcs. At the U.A. Festival, she confronted musical insecurities by leading Class 1-A's band as vocalist and bassist, performing "Hero Too" to inspire Eri and the school, cementing music as heroic expression. During the Provisional License Exam, she teamed with Tsuyu Asui and Mezo Shoji to rescue Momo from Saiko Intelli, showcasing teamwork. In the Final War against All For One, she resisted psychologically despite terror, inadvertently sparking rebellion among his vestiges. Her left ear and jack were destroyed, symbolizing sacrifice and resilience. Post-war, she adapted via prosthetics while retaining abilities. Eight years post-war, she graduated as the No. 30 pro hero, running her own agency near a prominent hero's base. Mentoring Eri, she balances hero duties with a music career. Physical changes include greater height and slightly longer hair, while her updated costume has streamlined amplifiers and black nail polish. Relationships stay central, including her bond with Momo and camaraderie with classmates like Kaminari, whom she nicknames "Jammingway."