Sakura would probably be there too. She might be the one to find Naruto when he's shrunken and in trouble. And Kakashi Sensei, he could play a role in training Naruto to control his shrinking ability or using it in battle strategies.
Obviously, Naruto would be one of the main characters. He's the one being betrayed. From RWBY, Ruby, Weiss, Blake, and Yang are likely to be involved. They are the central characters in RWBY, and if there's a betrayal of an outsider like Naruto, they would probably play a significant role in it.
The main character is Naruto for sure. When it comes to the Anbu, there could be some new and original Anbu characters created just for this fanfiction. They could have unique abilities and personalities. Naruto's relationship with these made - up Anbu characters could be really interesting. He might prank them in ways that play off of their individual quirks. For example, if one Anbu is really proud of his speed, Naruto could set up a prank that makes it seem like he's much slower than he thinks.
Naruto would probably be a central character. Given that he is the protagonist of the original series, in a fanfiction about the power of darkness, his reaction to this new and dangerous power would be crucial. Sasuke is also likely to be involved. His own struggle with power and his complex relationship with Naruto could be further explored in the context of the power of darkness. Kakashi, as a mentor figure, might play a role in guiding or trying to prevent the younger characters from being consumed by the power of darkness.
Well, obviously Naruto and Sasuke are the main ones. Since it's about Naruto absorbing Sasuke, their relationship is at the core. But also, characters like Kakashi could be involved. He might be the one guiding Naruto on how to control his new powers or trying to understand the implications of this strange occurrence.
Kakashi could also be an important character. He has a lot of experience and wisdom. When Naruto gets high, Kakashi might be the one to guide Naruto through this strange state, using his own past experiences and knowledge of different ninja techniques. And then there's Jiraiya. Given his relationship with Naruto, he would surely be involved, perhaps trying to use his own unique jutsu to help Naruto come back to normal.
The other Konoha 11 members would likely be involved too. They might be split in their opinions. Some would firmly stand by Naruto, while others might be swayed by the village's reasons for denying him. Hinata, for instance, would probably be one of Naruto's biggest supporters and might even try to fight against the decision in her own way.
Kakashi could be involved as well. As Naruto's mentor, he would likely be concerned about Naruto's well - being and how he is handling the fusion. He might try to guide Naruto in controlling the power and also protect him from those who would seek to take advantage of his new - found strength.
Obviously Naruto himself. He's the main character of the series so he's bound to be involved. Then there's Sasuke, his rival. They often get into all sorts of situations together, and a drinking game would be no exception. Sakura might also be there, trying to keep Naruto and Sasuke in check while also joining in on the fun.
Hinata would also play a major role. Since she has deep feelings for Naruto, she would be devastated by his amnesia. She might try to use their shared memories, like the time she confessed her love to him during the Pain attack, to jog his memory. And the Akatsuki members could also be involved in some cases. If Naruto's amnesia was caused by their actions, they might be the antagonists in the fanfiction, or they could also be trying to use his amnesia for their own purposes.
There could be new characters specific to the village where he becomes Kamikage. For example, some powerful shinobi clans within that village. Their leaders would be important as they could be Naruto's allies or opponents. Also, the previous Kamikage's advisors might still be around and play a role in guiding or challenging Naruto. Maybe an old sage - like figure who has deep knowledge of the village's secrets and helps Naruto understand and respect the village's heritage.