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.
Anko could also be included. She has a wild personality, and her presence in the Anbu could create some interesting dynamics. She might be involved in some undercover work with Kakashi, and their different approaches to the mission could lead to both conflict and cooperation.
Yamato could be a great addition. He was also part of the Anbu at some point. He could be a junior member who looks up to Kakashi and learns a lot from him. Their interactions could be used to show different aspects of the Anbu's hierarchy and training methods.
Obviously, Sakura herself is a must - include. Then, characters like Kakashi could be involved as he has Anbu experience. Naruto and Sasuke might also make appearances, maybe Naruto trying to help Sakura in her Anbu - related adventures, and Sasuke being a bit of a wildcard. Additionally, some original Anbu characters could be created, like a veteran Anbu agent who becomes Sakura's mentor in the Anbu world.
In Anbu fanfiction, Kakashi is often depicted as a highly skilled and mysterious figure. His past experiences in Anbu shape his character, making him more reserved and calculative. Sakura, on the other hand, might be shown as growing in strength and independence while in the Anbu setting. She could be learning from Kakashi's expertise and trying to prove herself in this more dangerous and secretive organization.
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 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.
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.
Naruto himself could be a great crossover character. Since Kakashi is his mentor in the original series, seeing them interact when Kakashi is a kid could be really interesting. They could have a different kind of dynamic, with Naruto perhaps being the more experienced one in some aspects. Another potential character is Goku from Dragon Ball. The contrast between Kakashi's ninja skills and Goku's martial arts and superpowers would create a really exciting crossover.
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.