Iruka - sensei is a character that can show up. Since he was important in Naruto's life, he could play a role in the girl's upbringing too. He might help with her education in the ninja academy. Also, the Akatsuki members could be antagonists in some stories. Their actions might force Naruto to protect the girl more fiercely, and this would drive the plot forward as Naruto battles against them to keep the girl safe.
Sasuke often appears. Since he is Naruto's rival and friend, his relationship with Naruto might be affected by the Kyuubi's influence on Naruto. Kakashi could also be there, as Naruto's teacher, he might notice the changes in Naruto due to the Kyuubi's new role in his life.
The street kids themselves would be main characters. They could be a diverse group with different personalities and backstories. There might also be Naruto's friends like Sakura and Kakashi who could play important roles. Sakura could help with the kids' medical needs, and Kakashi could offer his wisdom in training the kids.
Hinata could also be a common character. She may try to help Naruto secretly, or be heartbroken by his banishment and strive to change the village's decision. Another character could be Kakashi. He might be one of the few who believe in Naruto's innocence and try to find a way to bring him back to the village.
Jiraiya is often a common character. Since he was Naruto's teacher and had knowledge of sage training himself, he might appear in the fanfiction to guide Naruto further. Another one could be Kakashi. He is always looking out for Naruto and could be involved in the training in some way, like providing strategic advice.
Sasuke could be a common character. He might be in a situation where he has to choose between helping Naruto or following the village's orders when Naruto is on the run.
Sakura can also be a common character. She could be worried about Naruto and try to find him. Maybe she has her own reasons for wanting to bring him back, like her feelings for him or her loyalty to the village.
Jiraiya is another character that could be present. As Naruto's mentor, he would be concerned about Naruto getting the cursed seal. He might try to find a way to remove it or at least teach Naruto how to manage it without losing himself. Jiraiya's vast knowledge of ninja arts could play a crucial role in Naruto's struggle with the cursed seal.
Sakura could be a common character. Since she has a history with Naruto, she might be part of the harem in some fanfictions. Also, Tenten could be included as she is another female ninja in the Naruto universe. And Ino, with her strong personality, could also be written into the harem scenario.
Kakashi could also be a character in 'naruto and naruko harem fanfiction'. He can be the mentor figure, guiding Naruto and Naruko through different situations. His wisdom can influence how the harem relationships develop, for example, by giving Naruto advice on how to handle multiple relationships in a proper way.
Inner Moka is also likely to be in these fanfictions. Her more aggressive and powerful side compared to outer Moka can create different scenarios. For example, she might be initially hostile to Naruto but then gradually warm up to him as she sees his good qualities.