Kazuya Saotome is a 19-year-old electrical engineering student attending Ochanomizu Industrial University. He has a lifelong passion for building robots, with his primary personal project being a robotic squid named Ikariya, into which he attempts to program a functional artificial intelligence system. He resides in apartment 204 of a small wooden apartment building called Kasumi House. Kazuya is portrayed as a generally nice and hospitable young man, though he is also somewhat absent-minded and notably clueless when it comes to understanding the feelings of the girls around him. Despite being a dedicated student who regularly attends his college classes, his life is largely centered on his computer and robotics work, which he pursues with a quiet determination.

His primary motivation throughout the series is his deep-seated dream to build a true robot, inspired by the iconic character Doraemon. This ambition drives his tinkering with Ikariya and fuels his interest in advanced technology. His role in the story is set in motion by his long-time rival, the wealthy and egomaniacal Kotaro Nanbara. Nanbara, who is jealous of being constantly outdone by Kazuya in academic and technical projects, gives him a computer program that is actually a virus intended to destroy his work. While trying to fix the infection, Kazuya inadvertently accesses a secret website and accidentally orders a palm-sized cybernetic maid named May, which arrives with a massive, unpayable price tag. This event transforms his ordinary life as he finds himself responsible for May, whom he treats with kindness rather than as a piece of property, while also fending off attempts by Nanbara and the Cyberdyne Corporation to repossess her.

Kazuya’s key relationships are central to the narrative. His rivalry with Nanbara is one-sided, as Nanbara schemes against him while Kazuya remains largely unaware of the depths of his animosity, viewing him more as an eccentric acquaintance. A significant relationship is with Kasumi Tani, the athletic and tomboyish daughter of his landlord, who is a close friend and allows him to frequently delay his rent payments; she harbors romantic feelings for him, which he is slow to recognize. His relationship with the tiny cyberdoll May is the heart of the story. Unlike the corporations that see her as a product, Kazuya treats May with genuine care, constructing tools to help her with household tasks and striving to make her feel useful and wanted, which in turn fosters her deep loyalty and affection for him. Over the course of the series, other cyberdolls sent to retrieve May, including Sara, Rena, Kei, and Mami, also fall for his warmhearted and non-judgmental nature and choose to live with him rather than complete their missions.

Throughout the series, Kazuya undergoes a degree of character development. Initially portrayed as a somewhat isolated and focused engineering student, his life becomes more complicated yet more satisfying as he learns to navigate the chaotic household of cyberdolls and human friends who come to depend on him. He demonstrates a capacity for selflessness and responsibility, particularly in his determination to protect May from repossession and later from a deadly virus. A significant future revelation adds depth to his character: his humble work on the squid-like Ikariya is eventually revealed to be the foundational technology for the advanced M.a.i.d. Program, and he and his rival Nanbara are fated to co-found the Cyberdyne Corporation, which produces the cyberdolls seen in the series. As for notable abilities, Kazuya is a gifted programmer and engineer, skilled enough to build complex robotics and AI from scratch, even creating a makeshift recharging cable for May when her official equipment is broken. He also exhibits a trademark preference for a specific brand of milk.