Another possibility could be a new character created specifically for this fanfiction. This new character could have a special connection to the Blood Prison, perhaps being wrongfully imprisoned there. And as they navigate the prison, they build a harem around them, each member with their own backstory and reasons for being in the prison.
Naruto himself could be a likely main character. Given his determination and his ability to make friends, it would be interesting to see him in a harem situation within the Blood Prison. He could use his ninja skills to protect the harem members and try to break free from the prison's mysteries.
There could be some original Arrancar characters created specifically for the fanfiction. For example, a young and curious Arrancar who is new to the ways of her kind. She meets Naruto and is immediately fascinated by his different appearance and abilities. And then there's a more experienced Arrancar who has seen many battles. She initially sees Naruto as a threat but then realizes his good intentions and slowly falls for him, becoming part of the harem.
Obviously, Haren is one of the main characters. There might also be the prison guards who play significant roles in creating conflict or helping Haren. Another could be a mysterious inmate who has some knowledge about Haren's past or the secrets of the Blood Prison.
The main character is Naruto, as it's a Naruto - centered fanfiction. But in the Blood Prison setting, there could be other key characters. For example, the warden of the prison who might be a cruel or mysterious figure. Also, there could be a fellow inmate who has a special connection with Naruto, either as a friend or a rival. These characters play important roles in driving the story forward in the context of the dark and dangerous Blood Prison.
Well, obviously Naruto himself would be the central male character. For the female characters in the harem, Sakura could be one. She might start to see Naruto in a new light when he overcomes his blindness with such tenacity. Hinata could also be part of it. Her shy and loving nature could be a great contrast to Naruto's more outgoing and determined personality in this scenario.
Temari could also be a potential character. Given her status in the Sand Village and her strong - willed nature, she would bring a different dynamic to the harem. There could also be some original characters created specifically for the fanfiction to add more variety.
Well, one could be a female ninja from the Uchiha clan. She might be strong - willed and have the Sharingan. Another could be a gentle - natured girl from the Hyuga clan, with the Byakugan. And of course, there could be a foreign ninja who has her own unique abilities and catches the heir's eye.
In the Naruto world, Sakura could be a potential character in the harem. She's strong - willed and has her own set of skills. From the Yugioh world, Anzu could be part of it. She's kind - hearted and often supports the main characters. Another from Naruto could be Hinata, who is shy but also very loyal. And from Yugioh, Mai Valentine, as she has a bold and confident personality.
It could be one of the powerful and corrupt prison guards. They might have their own hidden agendas and see Naruto as a threat to their power or secrets within the Blood Prison. So, they start a scheme to make it seem like Naruto has betrayed everyone.
The warden of the Blood Prison could be the main antagonist. He might be a power - hungry and corrupt individual who sees Naruto as a threat to his control over the prison. So, he devises plans to get rid of Naruto, which ultimately lead to Naruto's death.
Some fanfictions might also feature the prison guards as main characters. They could be complex characters with their own motives and backstories, and their interactions with Naruto could drive the plot forward. For example, a guard who initially sees Naruto as just another prisoner but then comes to respect him.