Kim Min-kyu (Yoo Seung-ho) lives an isolated life due to a severe allergy to other people. He develops extreme rashes that rapidly spread throughout his body once he makes any form of skin contact. Jo Ji-ah (Chae Soo-bin) is a woman who is trying to make it in life by creating her own businesses. Kim Min-kyu who owns the KM Financial company which owns Santa Maria team headed by professor Hong Baek-kyun (Um Ki-joon). Professor Hong’s team has created a humanoid robot called Aji 3 which looks like his ex-girlfriend Jo Ji-ah.
CEO of KM Financial, Kang Ki-young, and his father try to sell the Santa Maria team to foreign investor, Martin, who secretly knows about the Aji 3 and wants to use it as a weapon. Hong Baek-kyun sends the robot to Kim Min-kyu to convince him not to sell the team. Before Aji 3 is delivered, the robot’s body is accidentally damaged. Hong Baek-kyun approaches Jo Ji-ah, asking her to pose as the robot, giving the team time to repair Aji 3. Jo Ji-ah agrees, and impersonates the robot under the supervision of the Santa Maria team and the robot’s computer brain.
Slowly, Kim Min-kyu falls in love with Jo Ji-ah, believing that she is Aji 3. He is disturbed by this, and reboots the Aji 3, erasing its memory. Professor Hong Baek-kyun replaces Jo Ji-ah with the real Aji 3. Jo Ji-ah, who has also fallen in love with Kim Min-kyu, leaves the city to work in her aunt’s restaurant, in an attempt to forget him.
Before the reboot, Aji 3 stores all the video footage and data from the trials with Kim Min-kyu in a secret cache. This cache gets hacked, revealing everything about Kim Min-kyu’s illness. This knowledge is used to stage a take-over of KM Financial, suspending Kim Min-kyu from the company and completing the sale of the Santa Maria team and Aji 3 to Martin.
Kim Min-kyu discovers that a human had replaced the robot, and has a sudden and violent allergic reaction, which nearly kills him.
Kim Min-kyu survives, submits evidence that Martin was involved in the murder of his parents, and restores the Aji 3 to the Santa Maria team. Jo Ji-ah slowly rebuilds trust with Kim Min-kyu. The Santa Maria team successfully launch the Aji 3 after changing its appearance.