Jase Ballenger is often a popular choice. His complex character, being a thief leader, offers a lot of scope for fanfiction. Writers can explore his leadership decisions and his inner thoughts.
Sly Cooper himself is obviously a very popular choice. His charm, skills, and family legacy make him a central figure. Bentley is also popular as he is the brains behind the operations and his gadgets add an interesting element. Murray is loved for his strength and his loyalty to the gang.
Keith is often a popular choice. His unique ability and his role in the original story make him an interesting character to explore further in fanfiction. Another popular one is Bethany, with her connection to different worlds and her own set of skills.
Joker is often very popular in fanfiction. As the leader of the Phantom Thieves, he has a lot of mystery and charisma. Writers like to explore his backstory further or put him in different, challenging situations where he has to use his wits and Persona powers in new ways.
Mo is often a popular character. He has a unique style and personality that makes him stand out. His confident attitude and great dance skills make him a favorite for many fanfiction writers to feature in their stories.
The vampire lead, often named something like Alexander or Damian, is usually quite popular. He's the brooding, mysterious type with a tragic past. Then there's the female lead, perhaps a human named Isabella or Sophia. She's brave and curious, which makes her a great counterpart to the vampire. Another popular character could be the vampire's mentor, an older and wiser vampire who imparts knowledge about the 'Dance of the Vampires' and vampire lore in general.
Aegon II Targaryen is often a popular character. His claim to the Iron Throne and his role in the Dance of Dragons make him a central figure in many fanfictions. Writers can explore his motives, his insecurities, and his actions during this tumultuous time.
Andy Herrera is often a popular choice. Her strong leadership skills and complex family background make for great fanfiction material. Writers can explore her relationship with her father, Pruitt, and how she balances her personal and professional life.
Hannibal is often a popular focus. His leadership skills and strategic mind make for great storylines. Writers can explore his past military experiences in more detail or create scenarios where he has to outwit an even smarter adversary.
Definitely Yu from the Investigation Team. His ability to form strong bonds with others and his leadership skills could make for some really interesting interactions with the Phantom Thieves. On the Phantom Thieves' side, Joker is a must - focus. His calm and strategic mind would contrast well with Yu's more empathetic approach. Their clashes and potential understanding of each other would be great to explore.
The main protagonist is often a popular choice. Their journey through the time twists provides a lot of room for character development and exploration. Also, any mentor - like characters can be interesting to focus on. They usually have more knowledge about the time - related phenomena and their backstories can add depth to the fanfiction. For example, if there's an old wizard who has been observing time for centuries.