Wang Joon is the lead in a drama, and Da Da and her team work on the show as the special effects makeup team. They don’t seem to get along at the set but in fact, Wang Joon and Da Da have been lovers for seven years in secret. Meanwhile, a humanoid called Zero Nine is getting ready for the final test.

Wang Joon wins the Best Male Lead Award. Da Da watches the show as she waits for him at his house. She is excited to see him win the award but also feels sad because she can’t congratulate him openly. Instead, she gets into embarrassing trouble. Meanwhile, Bo Won finds out about the client who will take Zero Nine.

Da Da kisses Zero Nine by mistake, and Zero Nine regards Da Da as his girlfriend. Da Da and Zero Nine get into a car accident, and Wang Joon tells Woong about his breakup. Meanwhile, Bo Won finds Zero Nine with Da Da. He tries to take him, but Zero Nine wants to stay with Da Da.

Manager Ko Ji Seok calls Bo Won and tells him that they only have a week before Diana finds out about Zero Nine. Zero Nine asks Da Da to name him, and Da Da calls him Young Gu. Young Gu looks through Da Da’s place and cleans up the place. While cleaning up, he throws away Da Da’s precious things by mistake.

Da Da gets replaced and works for Hwa Ni, a junior actor who is a rising star. Hwa Ni makes a scene, and Zero Nine appears and rescues her. Wang Joon sees Zero Nine and Da Da together, and he wants to know about their relationship. Meanwhile, Diana hurries Jung Hwan to bring Zero Nine to her.

Da Da gets a day off as Wang Joon’s shoot gets delayed. Da Da and Zero Nine clean the workroom together. Kyu Ri comes to Da Da’s place with outfits, and Zero Nine hides in the bathroom. Meanwhile, Wang Joon spends a day alone and looks back on his memories with Da Da. He goes to see Da Da and sees Zero Nine at her place.

Da Da tells Wang Joon that Zero Nine is her new boyfriend. Wang Joon gets jealous and makes unreasonable complaints about her makeup. Meanwhile, Da Da forgets to bring a dummy to the scene, and she asks Zero Nine to bring it in time. Zero Nine brings the dummy on time, but he gets hurt on his way.

It’s the last day of Zero Nine’s trial period. Bo Won comes to Da Da’s place to take Zero Nine. As they leave, Zero Nine finds a location tracker in Bo Won’s car. Bo Won and Zero Nine split up to run away, but Bo Won gets into an accident. Meanwhile, Da Da sees Wang Joon doing an interview at the TV station.

Da Da tells Zero Nine not to shut down the system, and they return home together. Ji Seok and In Hyuk meet Diana and tell her that they need a week more to deliver Zero Nine to her. Da Da and Zero Nine go to an amusement park for part-time jobs, and Wang Joon appears for an event.

Wang Joon and Da Da run into each other at the amusement park. Da Da leaves with Zero Nine, and Wang Joon gets upset as he sees them together. Da Da and Zero Nine get closer as they spend the evening at the amusement park. Meanwhile, Woong finds out about Wang Joon’s secret.

Wang Joon tells the director that he will join the show if Da Da’s team works with them. He wants to work with Da Da to get her back. Da Da and Zero Nine go shopping together, and Zero Nine learns about human traits. Meanwhile, Woong gets involved in a car accident.

Diana goes to Kronos Heaven and demands to see Zero Nine. Ji Seok manages to soothe her and gives her the tablet PC with details regarding Zero Nine. Woong needs to take a break for a month because of the accident. Meanwhile, Zero Nine finds out that Da Da is working with Wang Joon again.

Zero Nine meets Eun Dong at the station and applies for Wang Joon’s temporary manager job. Da Da goes to see Woong at the hospital, and Bo Won comes to see Zero Nine. Wang Joon gives difficult tasks to harass Zero Nine. Meanwhile, Manager Ko and In Hyuk get a clue to Zero Nine’s whereabouts.

Wang Joon takes Zero Nine to a gym to show off and harass him. Zero Nine gets an electric shock while using an exercise machine, and Da Da who was following them appears. As Da Da and Zero Nine leaves, and a mystery man tries to attack Da Da. Meanwhile, Da Da finds out that Wang Joon couldn’t come to dinner because of Woong’s accident.

Da Da is concerned about Zero Nine’s change. She wants to know why he wants to be loved all of a sudden. Zero Nine is engrossed in finding a way to be loved by Da Da. Wang Joon finds out that Da Da did go to the restaurant to see him. Meanwhile, Manager Ko and In Hyuk come to Da Da’s place again.

Manager Ko and In Hyuk try to take Zero Nine to Kronos Heaven. Wang Joon and Bo Won appear just in time, and they stop them from taking Zero Nine away. However, Zero Nine’s location is exposed, and he needs to find a new place to stay. Wang Joon lets Zero Nine stay at his place. Meanwhile, a flower box is delivered to Da Da.

Da Da finds out about the flower box and the reason why Wang Joon broke up with her. Wang Joon tells her to come back to him, and Da Da is confused. Zero Nine tells Bo Won about his change in heart, and Bo Won checks Zero Nine’s system. Meanwhile, Wang Joon gets a lead on the culprit who sent him the flower boxes.

Bo Won tells Ji Seok about Zero Nine having real feelings, but Ji Seok doesn’t believe him. In Hyuk tries to bring Zero Nine back but fails. Wang Joon tells Da Da to come back to him and proposes to her. Meanwhile, In Hyuk takes Diana to Da Da’s place to see Zero Nine.

Diana kisses Zero Nine, and he gets reset. He loses all his memories including the ones he shared with Da Da. Diana takes Zero Nine to her house and gives him a new name. Flustered, Da Da seeks for ways to get Zero Nine back. Meanwhile, Wang Joon sees Zero Nine with Diana.

Wang Joon asks Da Da to give him a chance to get her back. Diana tells Zero Nine about her hand and the accident. Zero Nine shows an error again, and Diana plans to take him to the head office to examine him. Bo Won finds out about her plan and asks Da Da to stop them from leaving.

Zero Nine recovers his memory of Da Da. He goes back to Da Da, and Zero Nine and Da Da spend a pleasant time together. Bo Won checks on Zero Nine’s condition and seeks a way to stop Diana together with Ji Seok. Meanwhile, Diana goes to Da Da’s place again to take away Zero Nine.

Bo Won manages to change the contract, and Da Da becomes the legal owner of Zero Nine. Diana calls the head office of Kronos Heaven and plans revenge. Zero Nine becomes a stuntman at the filming site, and Da Da finds out about Mr. Geum and his threat.

Da Da takes responsibility for Wang Joon’s accident and leaves the team. Wang Joon is eager to find the real culprit and investigates on his own. Bo Won is worried about Zero Nine having too much toll on his system. Meanwhile, Diana visits Kronos Heaven to get her new toy.

Zero Nine and Da Da spend the day together, but they hear people talking about Wang Joon’s accident. Zero Nine and Wang Joon run into each other as they both investigate to find the real culprit. Da Da goes to a middle school for a part-time job. Meanwhile, Wang Joon witnesses something suspicious about Zero Nine.

Wang Joon is suspicious of Young Gu’s identity. He looks for clues at Da Da’s place and finds out about Young Gu and Kronos Heaven. Da Da tells Wang Joon to understand her and keep Young Gu’s identity a secret. Meanwhile, Hwa Ni makes a scene at Wang Joon’s dressing room, and Eun Dong makes it into a scandal.

Wang Joon tells Da Da that a robot cannot be a lover like a human. However, Da Da and Young Gu show their feelings for each other. Bo Won asks Wang Joon to keep Young Gu’s identity a secret. Meanwhile, Diana comes to see Wang Joon. She invites him to her place and makes an offer regarding Da Da and Young Gu.

Wang Joon is locked up by Diana, and Zero Ten who looks like Wang Joon appears at Da Da’s place. Zero Ten pretends to be Wang Joon, but Young Gu notices his true identity. Ji Seok also finds out about Zero Ten, and Wang Joon takes tact and calls for help. Meanwhile, Zero Ten takes Da Da out to talk.

Diana threatens Wang Joon and Young Gu, and Zero Ten tries to hurt Da Da. Wang Joon finds Da Da and Zero Ten in the nick of time. Da Da and Wang Joon stop Zero Ten and escape from danger. Young Gu and Da Da reveal the truth of Wang Joon’s scandal and clear his name. Meanwhile, Wang Joon asks Woong to hold a press conference.

Wang Joon tells Da Da that he will wait until she comes back to him. Da Da and Young Gu prepare the memorial service for her father. Wang Joon, Woong, and Bo Won also join them. Diana plans to destroy Young Gu. Meanwhile, Young Gu stops with no reason at the filming site.

People find out about Young Gu’s identity. They are against Da Da and Young Gu’s relationship for various reasons. However, the situation makes their love deeper. In Hyuk finds out about Young Gu’s possible meltdown. Eun Dong comes to apologize, and Woong shows her feelings toward Bo Won.

Da Da and Young Gu are certain about their love and decide to become more confident. They go out on a date as ordinary couples. Kyu Ri is against their relationship, and Bo Won is upset about her not understanding him. After the shoot at the countryside, Wang Joon and the team go to a mansion as a vacation.

Kyu Ri tries to bring Da Da and Wang Joon back together and says harsh words to Young Gu. Wang Joon sees Da Da and Young Gu having a joyful time together. He tells Young Gu that he will give up on Da Da. Meanwhile, Manager Ko panics as he receives the data analysis of Young Gu.

Young Gu collapses because of the meltdown. He is overloaded as he learned human emotions with Da Da. Bo Won and Manager Ko try to find a way to save Young Gu. Diana seeks for revenge as she hears about Young Gu’s meltdown. Da Da is upset because there is nothing she can do for Young Gu.

Wang Joon finds out about Young Gu’s condition. Bo Won finds a component called the heart-cooler which can stop the meltdown. However, there is only one left at the head office. Wang Joon helps to get the heart-cooler from the head office. But Diana and In Hyuk intercept it.

Diana breaks the heart-cooler, and Da Da and others are frustrated. Young Gu wakes up at the lab and comes to see Da Da. Bo Won tells Young Gu about the broken heart-cooler and feels sorry for him. Young Gu tells Da Da that they should stay apart until they find the solution to his meltdown.

Bo Won and Manager Ko find another way to save Young Gu. The meltdown can be stopped if Young Gu gets all the data erased. However, his memories with Da Da will be gone. Bo Won insists that he should get reset to live, but Young Gu doesn’t want to forget about Da Da.

Young Gu decides to not be reset and spend his time left with Da Da. He lies to her about his condition, and Bo Won is upset about his decision. Young Gu goes to Wang Joon and tells him about his condition. He asks Wang Joon to take care of Da Da when he is gone.

Da Da still has no idea about Young Gu’s condition but after talking to Wang Joon, Da Da slowly comes to know about Young Gu’s condition. Meanwhile, Diana visits Young Gu before going back to New York, and asks him about his condition while apologizing for what she has done.

Young Gu’s condition gets worse, and he only has a few days left. Da Da and Young Gu go out for their last date to make happy memories. On the way home, Young Gu finally stops. Three years later, many things changed for Da Da and her friends. But she still misses Young Gu from time to time.

Da Da becomes the CEO of her company, and Woong and Bo Won is married. Wang Joon successfully finishes his drama and gets a chance to work abroad. He asks Da Da to go with him. Meanwhile, Bo Won takes Da Da to Kronos Heaven to see Young Gu for the last time.