A wise old mentor figure could be interesting. This character could be human and have a lot of knowledge about the world that they can pass on to the non - human protagonist. For example, a retired professor who has studied anthropology and can help the non - human understand human cultures.
A rival character is also a great addition. Maybe another non - human who has adapted to human society in a different way and is jealous of the protagonist's unique qualities. They could constantly try to undermine the main character's attempts to fit in.
A group of thieves could also be included. They might initially try to steal from the Prince of Darkness but end up getting caught in his web of power and secrets. Their street - smart skills and lack of scruples could create some interesting dynamics as they interact with the Prince and other more noble characters.
A powerful Raikage - like character as an OC would be great. This character could be extremely strong in physical combat and have a no - nonsense attitude towards protecting Kumogakure.
The nosy neighbor can be an interesting addition. They might have their own opinions on whether the couple should love their home or list it. Maybe they're jealous and want the couple to move, or they could be overly attached to the neighborhood and try to convince them to stay.
Well, if it's a crossover with Ultraman, Ultraman could be a great addition. His super strength and light - based powers would contrast well with the Jetman's abilities. They could have a friendly rivalry at first but then team up to face a powerful kaiju that is threatening both their worlds.
Definitely Obito. Since they have a long - standing connection, it would be interesting to see how their relationship played out during Kakashi's Anbu days. Maybe Obito was still alive and had his own secret missions within the Anbu that intersected with Kakashi's.
There could be a powerful wizard from a far - off land. This wizard has knowledge of ancient magic that could help or hinder the Son of Neptune. Also, a group of dwarven - like creatures who are excellent craftsmen. They could create special weapons or tools for the Son of Neptune's journey. Additionally, an exiled god who sees the Son of Neptune as a means to regain his former glory.
Obviously, Merlin himself. And Arthur could be in it too. Maybe Arthur doesn't initially recognize Tiny Merlin and there are some comical misunderstandings between them.
Definitely Sasuke. His rivalry and later friendship with Naruto is a central part of the Naruto story. In a fanfiction about a Naruto force, Sasuke's skills and his unique Sharingan abilities would be very useful.
Kakashi could also be a great addition. As a mentor figure, he could guide Sakura in understanding and controlling her newfound powers from her rebirth. And then there are the villains. Orochimaru could be interested in Sakura's rebirth if he senses some new and powerful chakra within her. He might try to capture her for his own experiments.
A scientist would be a great character. They could study the unique flora and fauna of the Jak and Daxter world and try to find ways to use their knowledge to help the inhabitants. For example, they might discover a new way to harness eco energy.