De Niro is an egg-shaped robot created by Miyu Kuonji, acting as her personal attendant and invention. He possesses advanced artificial intelligence granting him free will, independent thought, and an arrogant, short-tempered personality. Despite his bullying attitude, he demonstrates loyalty to Miyu as his master.

His design features a visible mouth and various integrated tools. He exhibits a peculiar compulsion to molest electronic appliances. De Niro also engages in karaoke singing, though his voice functions as a potent sonic weapon capable of causing brain damage. His concealed weaponry, including drills and rocket systems, deployable in combat, enables a "battle mode" primarily activated on Miyu's command.

Initially antagonistic towards Ren Uesugi, their relationship evolved into friendship following shared experiences. De Niro shows protectiveness over Miyu, often sleeping wrapped beside her bed and displaying displeasure when Ren spends time near her. He requires regular maintenance by Miyu to remain operational and is networked to the internet, allowing him to monitor matters like her financial transactions.

Within the Kuonji household, he is treated comparably to a family member despite his non-human status. His presence and unique abilities fuel household dynamics and incidents involving interactions with others.