His father Bowser could be a major character too. He might be searching for his son throughout the fanfic. There could also be other Koopa characters like the Koopalings. They could be on a mission to bring Bowser Jr. back or they might be secretly supporting his decision to run away.
In this fanfic, Bowser Jr. might run away because he's curious about the outside world. He has always been in the shadow of his father and the Koopa Kingdom. So, he takes off to explore different lands, face new challenges, and in the process, he could grow as a character. He might even make some unexpected allies or enemies along the way.
Sometimes, there could be original characters created by the fanfic writer. These could be other magical creatures or even some sort of mentor figure for Bowser Jr. who helps him develop his skills and understanding of the world around him, adding a new dimension to the relationship between Bowser and Bowser Jr. in the story.
One could be his father, Bowser. Bowser might be a main character as he could either be the cause of Bowser Jr.'s crying, like if he scolded him too harshly. Or he could be the one to comfort his son. Another character could be Luigi. Imagine Luigi somehow stumbles upon Bowser Jr. crying and has to decide whether to take advantage of the situation or be kind.
The Koopalings are also main characters. Each of them has their own distinct personality and abilities. For example, Ludwig is known for his intelligence and musical talent in some versions, and they all play important roles in whatever schemes they cook up.
The main characters are Bowser Jr. and Ludwig. Bowser Jr. is often portrayed as a mischievous and energetic character, while Ludwig is known for his intelligence and musical talents in the Mario universe.
In some fanfics, there might be a plot where Bowser Jr. tries to prove himself to Bowser. He might take on a difficult task on his own, like stealing a precious jewel from a well - guarded castle. This shows his growth and determination to be a worthy heir to Bowser. And it also adds a touch of family - like relationship exploration between them.
One possible theme could be family. As Bowser and Bowser Jr. are father - son, the fanfic could explore the dynamics of their family relationship. It could show how they support each other, or how Bowser is trying to raise Bowser Jr. to be a worthy heir.
One interesting fanfic could be about Bowser Jr. going on a solo adventure to prove himself to Bowser. He might encounter some of Mario's friends and have to use his wits to get out of tricky situations.
Well, it could be about Bowser Jr. losing a very important battle. Maybe he was trying to prove himself to his father, Bowser, but failed miserably. This failure made him feel so disappointed in himself that he couldn't hold back his tears. He might be crying alone in a corner of his lair, feeling like he let everyone down.
Mario could be one. Just imagine the chaos if Bowser Jr. swapped bodies with Mario. Mario's friends would be so confused, and Bowser Jr. in Mario's body could cause all sorts of trouble in the Mushroom Kingdom. Another character could be Luigi. Luigi's more timid nature compared to Mario would create a different dynamic if Bowser Jr. swapped with him. And Princess Peach is also a possibility. Bowser Jr. in Peach's body would be quite a sight, and it would turn the typical rescue scenarios on their heads.