Neiru Aonuma is a tan-skinned girl with striking emerald green eyes and dark brown hair, which she typically wears in a short braid pulled to one side. Her hairstyle is adorned with a set of pins and a light gray bow. As the series progresses, she adopts a new look, wearing her wavy hair loose with small dark gray ribbons on both sides of her head. A notable feature is the prominent scar running down the center of her back, a result of being stabbed by her sister.

Her usual attire consists of a long-sleeved gray dress with a white collar and cuffs, accented by a dark blue bow at the neckline. She pairs this outfit with white socks and brown loafers.

Neiru Aonuma is characterized by her calm, composed, and introverted nature. She generally avoids social interaction, only opening up to others once she has developed a sense of trust or camaraderie. Despite her young age, she demonstrates exceptional intelligence, discipline, and leadership, serving as the president of a major company. Her serious and driven disposition is further reflected in her actions most notably her decision to purchase a large quantity of Wonder Eggs and push herself to the brink of exhaustion in her determined efforts to save those trapped within them.

Neiru Aonuma’s past is marked by tragedy and mystery. She once had a younger sister who, for reasons never fully explained, stabbed Neiru in the back before taking her own life by jumping off a bridge. Neiru only learned of these events after waking up in the intensive care unit, and the resulting scar on her back continues to ache especially when she tries to suppress the memory. She finds temporary relief from this psychosomatic pain by aiding others through the Wonder Egg system, a journey that eventually leads her to meet Ai Ohto. The two form a close bond, and Neiru gradually opens up to the rest of the group, eventually becoming friends with the other protagonists, despite her initial reluctance toward Rika Kawai.

As the story progresses, it is revealed that Neiru, along with her deceased friend Kotobuki Awano, was created through artificial procreation in a laboratory. Selected for her exceptional genetic potential, Neiru was engineered by the corporation Japan Plati to possess extraordinary intelligence and unique capabilities. Neither she nor Kotobuki ever met their biological parents. In the anime’s special episode, it is further disclosed that the current Neiru is an advanced artificial intelligence constructed by Kotobuki using the personality data of Neiru’s original self. Now serving as the director of Japan Plati, she is assisted by Dr. Misaki Tanabe in overseeing the corporation’s operations.

In the Wonder Egg battles, Neiru Aonuma utilizes a unique, multi-functional weapon initially shaped like a compass, commonly associated with drafting and geometry. This compass can seamlessly transform into a variety of powerful weapons, including a sniper rifle, a greatsword, and an assault rifle, depending on the combat situation. Neiru demonstrates precise control over these transformations, adapting her weapon’s form to match her strategic needs during battle.

Additionally, Neiru possesses a pomander, an egg-like object that, once activated, hatches into a serpent-like creature she affectionately names Pinky. This creature accompanies her during her battles in the Egg World, providing support in her efforts to protect and rescue the souls within.