Hibiki Tachibana is a sixteen-year-old student attending the private Lydian Private Music Academy and serves as the central protagonist of Symphogear AXZ. She possesses a unique and powerful ability to summon a Symphogear, a form of ancient armor that allows her to combat supernatural threats. This power originated from a traumatic incident two years prior to the start of the series, when she was caught in a Noise attack at a concert. During the attack, a fragment of the third relic, the holy lance Gungnir, became lodged in her chest, fusing with her body and granting her abilities but also causing a condition known as "fusion症例第一号," or the first case of fusion syndrome.

Her personality is defined by an unyielding optimism and a kind-hearted, cheerful nature that makes it easy for her to form friendships and connect with others. She is an extrovert who is always eager to help those in need, and she strongly advocates for communication and understanding over unnecessary conflict. However, this cheerful exterior often conceals a great deal of personal pain. She is sensitive about her past and her family, particularly regarding her absent father, and she tends to avoid confronting her own issues, frequently hiding her sorrow even from those closest to her. This emotional depth means her feelings can heavily influence her actions in combat, sometimes leading to self-doubt or a loss of control over her powers.

Hibiki's primary motivation is to protect others and prevent the kind of tragedy she witnessed two years ago. She believes no one should have to accept death, a lesson she learned from the singer Kanade who saved her life at the cost of her own. In Symphogear AXZ, this drive compels her to join the military organization S.O.N.G., where she works alongside the United Nations to handle international disasters. Her specific mission in this season involves confronting a mysterious and powerful alchemical organization known as the Bavarian Illuminati, who are operating in the war-torn country of Val Verde with the goal of sparking a global revolution.

Her relationships with her allies are central to her character and development. Her most significant bond is with her best friend and roommate, Miku Kohinata, who serves as her emotional anchor and is often the only one who can see through her stoic facade to her true feelings. Hibiki describes Miku as her sunshine, and Miku's voice is frequently what pulls her back from the brink when she loses control of her powers. She also has a deep admiration for the seasoned Symphogear user, Tsubasa Kazanari, whom she originally followed to Lydian Private Music Academy as a fan. Her other key comrades include Chris Yukine, Maria Cadenzavna Eve, Kirika Akatsuki, and Shirabe Tsukuyomi, all of whom she fights alongside as part of S.O.N.G.. Her training under the powerful and wise commander Genjuro Kazanari has been instrumental in shaping her unorthodox fighting style.

Throughout the series, Hibiki undergoes significant personal growth. Initially, she struggles with the fragment of Gungnir inside her, which can cause her power to go berserk when her emotions run high. By the events of AXZ, she has gained greater mastery over her abilities. Her development includes learning to harmonize with others through techniques like the "S2CA Combination," which channels the energy from multiple Symphogear users' "绝唱" (Superb Songs) into a single, devastating attack, though it subjects her to the combined side effects of their powers. Her journey is one of moving from being a victim of circumstance to a wielder of immense power who must balance her desire to save everyone with the harsh realities of battle.

In combat, Hibiki is a unique fighter. Because the Gungnir fragment inside her is incomplete, she cannot manifest an "armed gear," which is a traditional weapon. Instead, she focuses all her energy into her fists and feet, engaging in powerful, close-range martial arts combat enhanced by her Symphogear's gauntlets and boots. Her fighting style is characterized by piston or rocket-powered punches that deliver devastating blows. Among her notable abilities are the "Vitalization" technique, which uses the combined power of six Symphogear users to form a giant arm for a single punch, and the "Glorious Break," a full-power attack utilizing the energy of seven users. A key development for her character is the ability to activate the "X-Drive," a powered-up form that unlocks her full potential. Later, through a process known as "黄金炼成" (Gold Refinement), she can transform her Gungnir armor into a powerful gold form to execute her ultimate technique, "TESTANMENT".