One common theme is friendship. Despite Popee's rather odd and sometimes cruel behavior in the original, many fanfictions explore the idea of him forming real friendships. For example, some stories show him gradually understanding the value of having a true friend.
One idea could be exploring Popee's backstory in more detail. Maybe he has a hidden past that led him to become the performer he is. Another idea is to introduce a new character to the fanfic, like a long - lost friend or a rival performer. This new character could bring new conflicts and storylines.
There's also 'Popee's Adventure Beyond the Circus'. This fanfiction takes Popee on a journey outside of his usual circus setting. It delves into his curiosity and how he copes with new environments. It's quite exciting as it shows Popee in situations we don't often see in the original work.
First, get to know the characters well. Watch the original content again if needed. Then, think of a simple starting point, like a normal day in Popee's life. For example, 'Popee woke up early in the morning, excited for the day's performance.'
To make the shift, start by analyzing the elements of fine art and trying to incorporate them into your cartooning. Experiment with different mediums like paints or charcoals. Also, take classes or look at tutorials to learn the specific skills needed for fine art.