She is a henchwoman working for the villainous Association Of Fathers group. They are led by a man who is disappointed by the lenience of modern day fathers; he wants them to act in a much more dominant way and be seen as the heads of the household, with their wives and children completely subservient to them. The group’s ultimate goal is to kidnap fathers and place their memories inside robotic replacements with much more dominant personalities. They also want to make some money by selling the robots to households around the country.
Ranran is seen in various different outfits throughout the movie, with characters who had seen her before being taken in by her new attire and not recognising her. Her many disguises include a short skirted salon outfit, a business suit and denim shorts and boots when she pretends to be giving out prizes. Her main outfit, when she isn’t disguising herself, is a sleeveless minidress and high heels.
Ranran is first seen posing as a woman working at a massage salon. Outside of the salon, she stops Shin-Chan and his father, Hiroshi, to take part in a questionnaire. Hiroshi initially dismisses her, until he actually notices her beauty, and then he is immediately drawn in by her. Ranran tells him he can come inside to have a free trial of the salon, telling him that it will help with his bad back. Inside the salon she starts massaging his shoulders and gives him something to smell to relax him. The aroma knocks Hiroshi out cold and a doctor then appears to take his memories and place them inside a robotic version, with the real Hiroshi being held by the evil Association Of Fathers group.
After spying on how the robotic replacement acts around the house, the leader of the group decides that the robot needs to have a much more dominant personality, and he instructs Ranran to go out and fix this. Ranran appears on a street corner in disguise as Shin-Chan is passing by and gives him a metal moustache as a prize for being the one millionth person to go around the corner. Ranran suggests giving it to his father for luck, which Shin-Chan does, but the attachment causes the robot to become much more domineering.
Eventually Shin-Chan manages to find out that his real father was kidnapped, instead of converted into a robot, like he and the family initially thought. Hiroshi is saved by his son, and the identity of the Association Of Fathers leader is revealed to be the local police chief. The leader captures Shin-Chan, his family and one of his female police officers, who was helping the family find out the truth. Ranran is with the leader when he reveals the group’s evil plan to replace fathers and profit financially at the same time. The leader tells his prisoners he is going to kill them, but before he can he is stopped by the robotic version of Hiroshi, who manages to reignite the fatherly side of himself to help release the captured heroes.
A fight commences, which includes Ranran chasing after Shin-Chan’s mother, but getting tackled by the female police officer before she can strike. However, Ranran quickly gets the upper hand in that battle, and uses her dangerously sharp nails to try and stab the police officer. Ranran is on top, with the policewoman close to meeting her doom, until Shin-Chan’s baby sister notices the evil woman’s shiny earring and is drawn in by it. The baby jumps on Ranran and starts rubbing her earring which causes Ranran to lose complete control due to being ticklish. During this moment of weakness, the policewoman arrests the evil Ranran and places handcuffs on her, with the villainess suffering the humiliation of being taken down by a baby tickling her.