Chika Amatori is a B-rank Sniper and a key member of the Tamakoma Second unit. She is a middle school student with short black hair, purple eyes, and a notably small stature for her age. Her Border uniform consists of a jacket with a sleeveless design, accompanied by holsters and knee-high boots.

Chika has a timid and reserved personality, rarely speaking at length and often keeping a distance from others. This behavior stems from traumatic past experiences: her friend Aoba Harukawa and later her older brother, Rinji Amatori, were abducted by beings known as Neighbors. Believing that people close to her get hurt or taken, she voluntarily isolated herself to avoid further loss. Despite her shy exterior, Chika is patient, serious, and capable of intense concentration. However, she suffers from low self-confidence and struggles to recognize her own potential. At her core, she is a kind-hearted individual who is deeply afraid of causing harm to others.

Her primary motivation is to grow strong enough to join Border's away mission to the Neighbor dimension. Her ultimate goal is to search for and rescue her missing brother Rinji and her friend Aoba. This desire drives her to endure rigorous training and participate in dangerous rank battles.

Within the story, Chika serves as a central figure due to her extraordinary and unique abilities. She possesses an immense trion gland, the energy source used by Border agents, which produces a quantity of trion that rivals or even surpasses that of a Black Trigger. This colossal trion reserve makes her a constant target for Trion Soldiers, which are drawn to her power, but it also grants her unparalleled firepower. Her sniper shots, particularly with the heavy Ibis rifle, are powerful enough to level buildings and bore holes through Border's fortified walls, earning them the nickname the Amatori Cannon. Her trion is so vast that enemy invaders from Aftokrator altered their mission to prioritize her capture, seeing her as a potential candidate to become their next god.

Her key relationships are central to her development. She shares a deep, trusting bond with Osamu Mikumo, a friend of her brother who promised Rinji to protect her. Osamu was the only person she trusted after her brother's disappearance. Meeting the protagonist Yuma Kuga marks a turning point; he is the first person besides Osamu she opens up to, and through him, she begins to warm up to others and become more sociable. She is mentored in sniping by Reiji Kizaki, a powerful A-rank agent who recognizes her potential and pushes her to improve.

Chika's character development is significant. Initially, despite her immense power, she could not fire her weapon at human or humanoid Neighbor opponents due to her fear of hurting others. This mental block forced her to use her power indirectly, such as destroying the environment to control the battlefield. Over time, through her experiences with Tamakoma Second and her desire to contribute to her team, she begins to overcome this hesitation.

In combat, she primarily uses the Ibis sniper rifle for its immense power, or the Lightning rifle for speed. Her notable abilities are enhanced by her high trion levels. She employs a trigger called Lead Bullet, which fires projectiles that do no damage but create heavy weights to pin down or slow enemies, a tactic that bypasses her fear of direct harm. She also uses Hound for homing projectiles and Meteor for large explosions. Furthermore, Chika exhibits a rare side effect that allows her to sense the location of incoming Neighbors, as well as the ability to conceal her own presence by calming her mind.