Ichigo could be the main character. Since he is the main protagonist in the original Bleach series, it would be natural for him to take on the central role in a fanfic involving dragons. He could have a special bond with a dragon, perhaps one that helps him unlock new levels of his power.
Uryu Ishida could be an unexpected but interesting choice as the main character. Given his Quincy heritage, in a 'bleach swinging pendulum fanfic' he could be at the center of a plot where the balance between the Quincy and the other factions is drastically altered. He might have to make difficult decisions to protect his people and also find a new place for himself in the changing Bleach universe.
It could be an ordinary human gamer who suddenly finds themselves as a Hollow in the Bleach world. They would have to adapt quickly, using their gaming instincts to survive.
Rukia could be the main character too. As a shinigami, she could be drawn into a strange gaming - like dimension. Her knowledge of the Soul Society and her ice - based zanpakuto powers would be useful in this new and unfamiliar environment. She could also have to deal with her own insecurities and past while trying to navigate through the gaming - inspired challenges.
Ichigo could be the main character. He has always been on a journey of self - discovery and growth in the Bleach series. Wishing upon a star could give him an extra boost or a new mission. For example, he might wish to become even stronger to protect his friends and family better. His complex relationships with other characters like Rukia, Orihime, and Uryu would add depth to the fanfiction.
Perhaps it could be a character who is a hybrid of Naruto and Ichigo. He has Naruto's determination and Ichigo's cool - headedness in battle. His unique heritage gives him the ability to use both ninjutsu and zanpakuto skills. This makes him stand out and draw the attention of female characters from both series, making him the main character in this harem - filled fanfiction.
A new character could be introduced as the main character. For example, a normal human from our world who is a hardcore gamer and suddenly gets transported into the Bleach world. They start with no knowledge of the spiritual world but quickly adapt using their gamer instincts. They could choose to side with different factions in the Bleach world, like the Soul Reapers or the Arrancars, based on what they think will give them the best 'game experience' in terms of leveling up and getting cool powers.
Aizen Sosuke is also a strong contender. His intelligence and manipulation skills, along with his unique powers, make him formidable. However, it's subjective as different characters have their own strengths at different points in the story.
At the beginning, Rukia was a rather cold and stoic character. She was bound by her duties as a Soul Reaper. But as the story progresses, she becomes more open and caring towards her friends, especially Ichigo. For instance, she starts to trust Ichigo more and more with the secrets of the Soul Society.
Well, in Bleach fanfiction, Karin and Toshiro's interactions can be really interesting. Karin's younger and more energetic nature can contrast with Toshiro's calm and collected self. Maybe they start off as just acquaintances in the fanfic, but as the story progresses, they find themselves having to rely on each other more. For example, they might be thrown into a situation where they need to work together to solve a mystery in the Soul Society.