"Hey, easy on the merchandise."
While she speaks and writes in a very informal tone, she is a knowledgeable and diligent researcher skilled in both studying the demon world and applying information about it to her various projects. She can deduce how the abilities of demons work and even replicate them. She apparently also possesses a very keen memory, being able to fabricate a fully functional replica of Lady's Kalina Ann without having any access to the original.
Nico is an extremely talented engineer. She created a series of prosthetic arms for Nero that can perform a variety of functions such as slowing down time, emitting shockwaves, and even replicating the abilities of the Devil Bringer.
She is also a fairly capable gunsmith, having created some of Lady's guns in the past.
Her access to her father's research also allowed her to train herself in the art of alchemy. She applied this knowledge to create a cowboy hat Devil Arm called Dr. Faust for Dante, using the Faust demon as the basis for the design. Her knowledge of arcane elements also gives her a keen sense of what materials might prove useful to her, often instructing Nero to pick up demon remnants so she can make use of their unorthodox properties.
Nico comes across as a cheeky Southern girl with a keen affinity for cybernetics. She takes great pride in her work, feeling that each of her designs are reliable and worth every dime. She seems to enjoy watching Nero slay demons, mainly because he's using her equipment in his hunts, though she does sometimes feel like he doesn't take sufficient care of her creations. Nico comes across as foul-mouthed and snarky and enjoys teasing Nero, affectionately calling him "asshole". She's very much a wild child, sporting extensive tattoos, dressing provocatively, and being a reckless driver.
Despite her rough appearance and coarse language, Nico is nothing if not friendly and exceptionally loyal to those she cares about. She willingly accompanies Nero to the giant demon tree in spite of her concerns about the dangers they would face there. She appears to get along well with Trish and Lady as well as Kyrie. Nico had also heard of Dante from her grandmother's stories and was instantly starstruck when she got to meet him.
She generally shows great respect for those who do work similar to her own, hence her admiration for her adoptive grandmother. She was saddened at Nero having to destroy the ancient demon weapon Artemis when he defeated the demon formed from it, describing its creator Machiavelli as a "legend."
Nico truly hated her father Agnus, due to him abandoning her and her mother. When she learned about his death from Nero, she felt relieved. In spite of her light-hearted attitude, she can be somber and empathetic, as shown when she spoke to Nero about their respective fathers. Nico and Nero treat each other like sister and brother.