Riruru is voiced by Yuriko Yamamoto in the original movie and Miyuki Sawashiro in the remake.
As one of the first scout units to take over Earth, Riruru comes from the faraway robotic planet called Mechatopia. Her main duty is to transport the war machine robot, Jill (who Doraemon and Nobita rename him to Zanda Cross). However, she is unable to locate the robotic parts, despite the act that all of them were transported. Riruru's search has led her from the North Pole to modern day Japan. She searches from the Nobi Household to the school area and asks various Tokyo's residents but to no avail.
On her way of searching the mountain area, she rescues Nobita from Micross, Suneo and Gian's new toy, by tampering it's electromagnetic circuit as she heard that Nobita is in possession of a very large robot, forcing Nobita to reveal secret of the Mirror World to Riruru. He brings her to Zanda Claus and returns the robot to her, although she's surprised why it isn't able to function automatically. Riruru thanks Nobita and asks him two favors, to allow her to borrow the Mirror Pool for a while, and to keep their meeting a secret. Nobita agrees to respect both of her wishes.
Using the Mirror Pool, Riruru is able to transport the massive robot army into the mirror world to use as a frontline base for conquering the Earth. When the plan is
accidentally discovered by Nobita and Doraemon, she promises not to harm them and offer him to join her in the world domination, to which they refuse. During the two's escape from the mirror world, an explosion subsequently destroys the Mirror Pool and seals the gateway.
When Nobita and Doraemon discover that the Mechatopian army has prepared to strike Earth, they formulate a plan with Gian and Suneo to change Zanda Claus' brainwave pattern to turn him into their ally. They then enter the mirror world through Shizuka's bathtub which Shizuka later follows them that evening. Shizuka wanders at the mountain area of the mirror world and found a damaged Riruru. Riruru attempts to strangle her but is stopped when Micross attacks her. Shizuka then brings Riruru to her house despite Micross's objection, and informs the gang when Nobita comes to rescue her from one of the enemy soldiers.
Suneo suggests that they should destroy her to prevent the enemy from discovering them but Shizuka and Nobita disagree with the plan as it's too cruel. Doraemon then proposes that they should repair her, and assigns thr task to Shizuka. Later that night, Riruru wakes up and has a chat with Shizuka about the legend of Emu and Amu, the first two robots of Mechatopia created by "the god" who planned to turn the human race into slaves. Enraged when Shizuka tells her that the opposite is for humanity, she attacks Shizuka, but then collapses due to injury. Despite the fact that she doesn't want to help Riruru anymore, she returns to nurse her anyway.
The next day, Doraemon comes up with a plan to lure the Mechatopia Army into the mirror world which requires Riruru's computer function to be put to sleep for 24 hours in order to prevent any mistake. This requires Shizuka to have Riruru take a pill that would do just that. She does it without fail, but when she left the room, Riruru spits out the pill and escapes. Nobita eventually finds Riruru near the ruins of a subway and asks her to return, to which she refuses. He then threatens to shoot her if she resists, but ultimately he doesn't. Riruru then paralyzes Nobita (in 2011 remake, this happens to Pippo), and is soon found by the Mechatopia Army.
The Robot General demands that Riruru explains to him why there are no humans and where they has gone to. Riruru, however, refuses to answer him and instead asks for the world domination plan to be stopped as humans also have feeling and heart like them. Angered, the General hits her, electrocutes her and then orders 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 behavior 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 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.
In the remake, Riruru's hair color was changed from salmon to pink, and her eyes were also changed from teal blue to sky blue.