Riruru came from the faraway robotic planet, Mechatopia, as one of the first scout units to take over Earth. She came with the task of transporting the war machine robot, Jill (who Doraemon and Nobita renamed Zanda Cross). However, after all the parts were transported, they disappeared. Riruru's search has led her from the North Pole to modern day Japan. She had searched from Nobita's house to school and asked Tokyo's residents, but to no avail.
On her way of searching the mountain, she rescued Nobita from Micross, Suneo and Gian's new toy, by tampering it's electromagnetic circuit because
she heard that Nobita is in possession of a very large robot. This forced Nobita to reveal the Mirror Pool secret to Riruru and bring her to Zanda Claus and return the robot to her. Riruru thanked Nobita and asked him two favors, to allow her to borrow the Mirror Pool, and to keep the event a secret. Nobita agreed to respect both of her wishes.
Using the Mirror Pool, Riruru was able to transport the massive robot army into the mirror world to use as a base for conquering Earth. When the plan was
accidently discovered by Nobita, she promised not to harm him and ask him to join her in the world domination, to which he refused. During the escape from the mirror world, an explosion subsequently destroyed the Mirror Pool and sealed the gateway.
When Nobita and Doraemon discovered that the Mechatopian army had prepared to strike Earth, they formulated a plan with Gian and Suneo to change Zanda Claus' brain wave pattern to turn him into their ally. They then entered the mirror world which Shizuka later followed them that evening. Shizuka wandered at the mirror mountain and found Riruru. Riruru attempt to strangle her but is stopped when Micross attacked her. Shizuka then bring Riruru to her house and inform the gang when Nobita came to rescue her from one of the enemy soldier.
Suneo suggested that they should destroy her but Shizuka and Nobita didn't agree as they thought it to be too cruel. Doraemon then said that they would repair her, and assigned this task to Shizuka. Later that night, Riruru woke up and had a chat with Shizuka about the legend of Imu and Amu, the first two robots of Mechatopia created by "god" who planned to turn the human race into slaves. Enraged when Shizuka told her that the opposite is for humanity, she attacked Shizuka, but then collapsed. Despite the fact that she didn't want to help Riruru anymore, she returned to nurse her anyway.
The next day, Doraemon had come up with a plan to lure the Mechatopia Army into the mirror world which required Riruru's computer function to be put to sleep for 24 hours in order to prevent any mistake. This required Shizuka to have Riruru take a pill that would do just that. She did this without fail, but when she left the room, Riruru spit out the pill and escaped. Nobita eventually found Riruru near the ruins of the subway and asked her to return, to which she refused. He then threaten to shoot her if she resisted, but ultimately he didn't. Riruru then paralyzes Nobita (in 2011 remake, this happens to Pippo), and was soon found by the Mechatopia Army.
The Robot General then demanded that Riruru explain to him why there were no humans and where they had gone to. Riruru, however, refused to answer him and instead asked for the world domination plan to be stopped as humans also have feeling and heart like them. Angered, the General hit her, electrocuted her and then ordered Riruru to be imprisoned (executed in 2011 remake) as a traitor. In the remake, a firing squad was about to kill her, she asked one last time to stop the invasion. The General gets angry and orders to kill her right then and there. Riruru was later rescued by Nobita and Doraemon (and Pippo in the remake) and they brought her back to Shizuka's house. Riruru asked to be locked up as she still couldn't decide what she should do. She was shrunk by Doraemon's small light, then locked in the bird cage (image below) in Shizuka's house.
While the boys had their battle at the Akai Lake, Shizuka got an idea from Micross that they should go to meet the "god" who created Imu and Amu, who was a scientist who had given up on humanity. The scientist explained that the reason for the malevolent behaviour of the robots was because he implanted the "competitive instinct" which made the robots' minds too similar to that of humans. The scientist then attempted to change the program, but couldn't since he was dying. Riruru then asked to be the one to finish the program, while Shizuka tended to the scientist.
When the program was finished, all the robots in the mirror world began to disappear. However, the same thing was also happening to Riruru. She told Shizuka that she would be reborn and she wished to be an angelic robot, to which Shizuka replied that she was now an angel. Riruru then shed tears and found it strange for a robot to experience something like this. Shizuka then asked for Riruru to hold her hand and promised that they would be friends, no matter where or when she would be reborn, to which Riruru promised before she disappeared. Shizuka then returned to tell everyone about Riruru's sacrifice.
Sometime later, in the classroom, Nobita wondered if Riruru had been reborn yet, then look out of the classroom window. He then saw Riruru who waved her hand at him, indicating that she was finally reborn and had become an angelic robot like she had wanted to be. Nobita then ran off to tell his friends.
Everything is still the same, except that Riruru saved and repaired Pippo, who was damaged for singing, even though he was designed to be a labor robot. Essentially, Zanda Claus' brain was given a personality.