Puzzle?! Mystery Appearance of Pretty Girl

'''Puzzle?! Mystery Appearance of Pretty Girl (Shock?! The Appearance of a Mysterious Beauty''' in the subbed version) is the fifth episode of Robot Girls Z.

Plot
A mysterious new girl named Minerva X appears to Z-chan doing things like give her takoyaki and calls her "sister". Gre-chan finds her suspicious especially after Minerva forces her to work in place of Z-chan. Despite her sweet first look, Minerva holds a scheming secret that Gre-chan has to find out as the simple minded Z-chan can't figure it out for herself.

Synopsis
At the park, Robot Girls Team Z are enjoying takoyaki with Z-chan noticing that Gre-chan's are bigger and asked for one which Gre-chan refused. A girl then approached them and gleefully charged at Z-chan while destroying Jack's cart in the process and calling her 'onee-chan'. The other girls are puzzled by this especially Gre-chan. The girl introduces herself as Minerva X, a Robot Girl designed to be a partner for Z-chan. Gre-chan finds her suspicious though. When Z-chan leaves to get ice cream, Grenda-san compliments on having a new companion. Minerva however with a scary face says that her only 'onee-chan' is Z-chan while going back to her cute face as Z-chan comes back. Gre-chan seems jealous and looks with an angry face at Minerva who returns with a face of her own.

At a gas station, the Robot Girls fill up a car with Photonic Energy. Minerva doesn't like the fact that Z-chan is working like that and tells Grenda-san off in a rude way. Minerva states to have Gre-chan work after jamming the nozzle in her mouth and go on a date with Z-chan. Gre-chan however gets angry and refuses to oblige. Minerva uses this to look innocent and cling to Z-chan as a scared girl. Z-chan tells Gre-chan off and goes to the break room with Minerva as Minerva makes a face at the other girls. Gre-chan seems saddened by this. Baron Ashura and the Mechanical Beast Girls are hiding in the bushes complimenting that their plan to use Minerva X and isolate the Robot Girls is working.

Inside the break room, Z-chan tends to Minerva. Ashura uses a notepad to give the command to get to Z-chan. Minerva attempts to come physically close to Z-chan. Ashura was surprised by this and tried to get her Mechanical Beast Girls not to look. Minerva undresses Z-chan and later herself. The plated bra and her shirt reveal that she's flat chested. Minerva then revealed that 'she' is actually a boy which made Z-chan quite shocked. Before anything else could be done, Gre-chan barges in and tears down the break room. Z-chan runs to her teammates where Grenda-san reveals she knew that Minerva was actually a boy. As Minerva attempts to get back to Z-chan, Gre-chan gets in her way. They start to fight by grabbing their faces before Minerva unleashes a Rocket Punch that Z-chan blocked for Gre-chan. After falling over, Z-chan cuddles Gre-chan to both of their relief. Minerva seems saddened by this and leaves. The watching Ashura and Mechanical Beast Girls are met by Grenda-san who knew their plot and sent them flying with an explosion.

The next day, the Robot Girls are enjoying donuts with Z-chan asking for some of Gre-chan's which she is about to do until Minerva falls from the sky and destroys Jack's cart again. Z-chan is shocked at this thinking Minerva gave up. Minerva revealed that he would come to get Z-chan's love no matter what. Gre-chan starts to fight with Minerva again.