Eve Neuschwanstein is the female lead of the story and a central figure within the resistance group fighting against the Simeon Corporation. Her background is deeply rooted in scientific experimentation; she was created as part of the Eve Project. Her original name was simply "N," designating her as the fourteenth specimen, which was later expanded into the surname Neuschwanstein. She was designed with a specific, engineered purpose: to be the "partner" of Adam Blade, as his unique DNA made it impossible for him to reproduce with an ordinary human. In a deeper biological twist, she is the younger sister of Kasumi, an assistant to the scientist Gido. After a tragic accident, Kasumi transferred half of her brain to Eve to save her life, and Adam Blade later also gave a part of his own brain to her, making her survival intrinsically linked to them both.

In terms of personality, Eve is most notably characterized by her incredibly poor memory, especially for names. To compensate for this, she assigns nicknames to everyone she meets, most famously calling the protagonist Cruz Schild "Yamada" and another ally, Suetsugi, "Uchida". Despite her immaturity and impatience, which can make her seem like a typical young girl, she is deeply loyal and a fierce combatant. She harbors a secret sense of shame about her inability to remember names, wishing she could get them right. Her core motivation is protecting her friends, particularly Blade, who is her closest companion and the first person she befriended.

Throughout the story, Eve plays the critical role of Blade's partner and the group's primary powerhouse, often engaging in direct combat against the powerful enemies of Simeon. Her most significant relationship is with Adam Blade, whom she met in childhood and for whom she feels a profound connection. She develops a strong bond with Cruz, even though she cannot remember his real name, and he often uses his intelligence to aid her, such as freeing her from mind control. This mind control incident represents a major point of development for Eve. She was captured by the Simeon Girl Force and forcibly brainwashed into becoming a slave and a member of their unit, an event that stripped her of her will and personality. She was later restored to her true self thanks to the efforts of Cruz and Blade. Following a massive explosion, she was found severely injured and required a lengthy recovery, proving that even her formidable resilience has limits.

Eve's notable abilities come from her Fragment, a superhuman power known as Doppelganger. This ability allows her to transform her body into any shape or form she can imagine. She can morph her arm into a massive drill for offensive purposes, change her entire appearance to impersonate another person, or even transform into inorganic substances like a wall. This power is extremely versatile and powerful, with the antagonist Arclight even comparing its potential to that of a legendary "Missing Link". However, the use of Doppelganger has a significant drawback: it consumes an enormous amount of energy. To counteract this, Eve constantly drinks a high-calorie energy beverage called Super Gel Dero Doro Drink, which contains 5000 kilocalories per serving. Her need for fuel is her primary weakness in battle, though it was temporarily neutralized when Simeon installed a device inside her that provided an unlimited supply of calories.