Eva possesses long blonde hair worn with a blue headband. She appears to be at the age of a high schooler and wore a fall Japanese high school uniform. Eva possesses unique looking eyes that appeared in a few characters designed by Shotaro Ishinomori (including Helena), lacking sclera, have a sparkling look, and are colored dark blue.
When revealed to be a cyborg, 0015 wears the uniform worn by the other High-Teen cyborgs, a black version of the 00 cyborg uniform with silver buttons, a white scarf and two white belts, and red seams on the shoulders and boots.
In her civilian disguise, Eva presents herself as kind yet reserved, although the shyness is caused by several things happening inside her head. She is curious about Miki Makimura's family and life, as she herself is very sheltered and wants to know what it is like for someone with an average life. Ultimately, the real reason Eva got close to Miki was so that she could use her as bait to lure Akira Fudo (aka Devilman) to Dr. Adams' base. In spite of this, Eva still cares about Miki and does not allow her to get hurt.
Eva is driven to free her fraternal twin Set from Dr. Adams and is willing to do whatever it takes, whether it harms her or others. Not enjoying his comatose state, Eva plays both sides including the demons aligned with Dr. Adams in order to save Set. This continues even after Set is fused with Atun, trying to reason with him at every turn and even risk her life with astral projection.
Eva is stated to be an Intentional Mutant possessing psychic powers that are brought out through her cybernetics. Like the other High-Teen cyborgs, she possesses an accelerator to move at mach speeds. Eva also incorporates a psychic aura when using her accelerator, allowing her to blow back obstacles in her path. She also had the self-repair functions of the other High-Teens which allows her to recover from her injuries quickly.
Eva's psychic powers include the common stock group of telepathy and telekinesis. Her telekinesis allows her to not only move objects but can also cause opponents to be rendered completely inert, as if frozen in place. She can also fire off telekinetic force shock waves in the form of yellow bolts, this causes Eva's eyes to turn red. Eva can also use the telekinetic force to create force fields, but against a greater psychic output it can be disrupted. Eva's final ability is astral projection, but due to how physically taxing it is, she requires help from another psychic such as 001 to move long distances and maneuver while still being no less exhausting.
Eva had come to Japan under instruction from Dr. Adams to track down the human who had overtaken the Demon Hero Amon and bring him to the base to get Atun to awaken and merge with the comatose Set. Going undercover as a transfer student to the human Akira Fudo's school, Eva befriends Miki sharing her relationship with her brother and Set's condition.
When demons led by Lilith appear, Eva reveals herself as 0015 to the demon after Miki passes out from shock. Eva brings Miki to Adams base where she oversees the process where Set is fused with Atun becoming the Cyborg Daemon. However, seeing that Atun has taken over her brother's mind, Eva despairs at the monster her brother has become.
As Atun and Devilman clash, Eva calls out to everyone about what had transpired trying to convince 0013 to abandon Black Ghost's work to no avail. With no other option left, Eva works with Dr. Gilmore to set off an EMP wave that disrupts the self-repair system of the High-Teen Number Cyborgs. But this causes the Cyborg Daemon to become a new form known as Azazel. To end the conflict once and for all, Eva gets help from Cyborg 001 to use her astral projection to pull Set's consciousness out of Azazel and succeeds.
Eva's name contains different references to biblical figures. Her first name, Eva is the Latin form of the Hebrew name Chavah/Havah, meaning "life" and is a derivative of Eve, the significant other of Adam who was created by one of his ribs. Due to being influenced by an outside force, Eve is also the one who caused her and Adam to fall from Paradise. This is similar to how Eva became a cyborg due to Dr. Adams and it was her actions that caused his plans to fall apart. Maria is a common name used in the bible, with the Old Testament character being the sister of Moses, the man who built an arc to preserve the species during the Great Flood. Likewise, Maria is the Latin form of Mary, the name used for the Virgin mother of Christ and for Mary Magdalene. Both of these reference her relationship with Set.
Her surname Parallels means someone who is similar to another with Eva's design being based on characters designed by Ishinomori. The derivative, Pallares is Spanish for extract, remove, and similar words, referencing how Eva wants to save her brother Set by getting Atun out of his body. On an unrelated note, surname being of Galician origin.
- Eva's design appears to be inspired by the earliest design for the character Rina Hirokoji in Ishinomori's series Blue Zone, which ran in 1968 and was left unfinished.
- In early concept art, she had a drastically different character design and inspiration, with her lacking the sparkly eyes and having more standard-style ones, along with her hair being tied off into two large high ponytails. The High-Teen Number uniform was also primarily red and black (as opposed to black and white/silver), with the white portions being limited to the contrasting parts, while the cyborgs' boots would also have the red buttons on them.
- In an attempt to shield the identity of Eva as 0015, which was nevertheless spoiled by multiple sources (the theatrical brochure and light novel and hinted at by her voice actress), any references to "0015" in the second episode depict the cyborg as a masculine placeholder silhouette, seemingly bald and with a glowing red eye.
- Despite of what it might seem, there is actually no clear evidence suggesting that she had died after the final battle. During the aftermath, the last scene of Eva is that of her sitting on the edge of the formerly hidden facility- this does not confirm her fate as deceased as it was never shown that she had deactivated or not (similar to Edward's case) and thus is left up to the audience's interpretation.