There could be a fanfic where an OC is a long - lost sister of one of the main characters in Powerpuff Girls Z. She has been hidden away for some reason and now returns with a special mission. This would create a lot of emotional drama as well as new plot twists in the story.
One interesting storyline could be an OC (Original Character) who has a unique power that the Powerpuff Girls Z initially mistake for a threat. For example, an OC with the power to control plants might start making the city overgrown with beautiful flowers and trees. The Powerpuff Girls Z think it's chaos at first, but then realize the OC just wants to make the city more beautiful. Another could be an OC from another dimension who comes to their world and has to learn how to fit in while also helping the Powerpuff Girls Z fight a new villain. There might also be a story where an OC has a power that complements the abilities of the Powerpuff Girls Z, like an OC who can manipulate time a little bit and helps them prevent disasters before they happen.
One interesting storyline could be the Powerpuff Girls Z facing a new, super - powerful villain from another dimension. This villain has powers that are the opposite of theirs and can manipulate time, causing chaos in Townsville. Another could be a story where they lose their powers temporarily and have to rely on their wits and teamwork to save the day. Maybe they team up with some of their former enemies who also realize the new threat is too great for them to handle alone.
One popular storyline could be a male OC who has unique powers and teams up with the Powerpuff Girls Z to fight a new, powerful villain. For example, he might have the power to control time, which helps them in a battle against a villain who can manipulate reality. Another could be a story where the male OC is from a different dimension and has to adjust to life in Townsville while also using his powers to help the girls. He could introduce new technologies or ways of fighting that the girls haven't seen before.
In some fanfictions, there could be a plot where the powers of the Powerpuff Girls Z combine in a new way when they are in the RWBY world. For example, their chemical X - like powers could interact with the Dust in RWBY to create unique abilities. This could lead to them training the RWBY characters in this new form of power usage.
Well, it's hard to say exactly who the most popular ones are as it can vary from person to person. But some OCs that are often liked are those with really cool and unique powers. For instance, an OC with the ability to control elements like fire, water, earth and air all at once is likely to be popular. They can bring a whole new level of action to the fanfic.
One idea could be a story where the Powerpuff Girls Z and the Rowdyruff Boys Z have to team up to face a new super - villain that neither of them can defeat alone. Maybe this villain has powers that are a combination of all their weaknesses.
Maybe there's a device that combines the chaos emeralds' power with Chemical X. This causes a strange rift in the dimensions, bringing Sonic and the Powerpuff Girls together. They have to work together to reverse the effects of this strange combination. Sonic uses his speed to gather the scattered chaos emeralds, and the Powerpuff Girls use their powers to keep the villains from interfering.
There could be a fanfiction where the Powerpuff Girls Z travel to an alternate dimension. In this dimension, everything is reversed. Their powers work differently, and they have to adapt quickly. They meet alternate versions of their friends and enemies, which makes for a really exciting and unique adventure.
One idea for a fanfic could be that Dexter creates a device that accidentally merges the worlds of Powerpuff Girls Z and his own. The Powerpuff Girls Z then have to deal with Dexter's crazy inventions while Dexter has to adapt to the super - powered world of the girls. Maybe they team up to fight a common enemy that is a result of the accidental merge.
One idea could be an OC who has a unique power like the ability to control plants. She could team up with the Powerpuff Girls to stop Mojo Jojo from creating a giant plant monster to take over Townsville. Another plot could involve an OC from another dimension who comes to Townsville seeking help because her own world is being threatened by a similar evil as in Townsville. The OC could bring new powers and a different perspective to the fight against the villains.