Kim Min-kyu lives a luxurious but isolated life due to a severe allergy to physical contact with other human beings. He develops extreme life-threatening rashes that rapidly spread over his body whenever he makes any form of skin contact. Jo Ji-ah is trying to create businesses based on her inventions, notably two networked heart-shaped lamps.
Min-kyu is the chairman and largest shareholder of KM Financial. He inherited his shares from his parents, who died in a car accident 15 years earlier. He was brought up by his father's friend and colleague, Hwang Do-won whose son, Hwang Yeo-chul , is the same age as Min-kyu and the CEO of KM Financial.
KM Financial owns the Santa Maria team. The team is headed by professor Hong Baek-gyun. Professor Hong's team has secretly created an advanced humanoid robot called AG3 (pronounced Aji 3), whose appearance he modeled on his ex-girlfriend Ji-ah (the sound of the robot's name is Ji-a [AJI 3] backwards).
Hwang Yeo-chul and his father Hwang Do-won try to sell the Santa Maria team to Bold Group, owned by a foreign investor, Martin, who has learned about the Aji 3 and wants to use it as a weapon. To convince Kim Min-kyu not to sell the Santa Maria team, Baek-gyun sends the robot to him as a demonstration. Just before the Aji 3 is delivered, the robot short-circuits and Baek-gyun asks Ji-ah to pose as the robot, giving the team time to repair Aji 3. Desperate for the 10 million won payment he is offering her, Ji-ah agrees, and impersonates the robot under the supervision of the Santa Maria team.
Gradually, Min-kyu falls in love with Ji-ah, believing that she is Aji 3. He is disturbed by this, since she is a robot to him, and "reboots" her, erasing the robot's memory. Baek-gyun then replaces Ji-ah with the real Aji 3. Ji-Ah, who has also fallen in love with Min-kyu, leaves the city in an attempt to forget him.
Min-kyu discovers Ji-ah's deception and that she had been pretending to be the robot, and has a violent allergic reaction that nearly kills him. Baek-gyun saves him and Min-kyu angrily breaks off his relationships and friendships with them all for their betrayal and for playing with his feelings. Ji-ah confesses everything to Min-kyu and says she loves him, and they rediscover their love, this time as humans.
Before the reboot, Aji 3 had stored all the video footage and data from the trials with Kim Min-kyu in a secret cache. This cache gets hacked, revealing everything about Min-kyu's illness. The knowledge is used to attempt a take-over of KM Financial, to remove Min-kyu as chairman and complete the sale of the Santa Maria team and Aji 3. Min-kyu manages to thwart the attempt at the last moment. He uncovers evidence that Hwang Do-won and Martin were involved in the murder of Chairman Park, and restores the Aji 3 to the Santa Maria team. 2 years later, the Santa Maria team successfully launches a new robot after changing its appearance, while they, along with Ji-ah, and Min-kyu (after completing the mandatory military service) are happily living their changed lives.
