Itachi might be involved. Even though he has his own complex backstory, in this fanfiction, his powerful abilities and knowledge could be used to try and stop Naruto from losing his humanity completely. And the yaoi aspect could come in as Itachi forms a deep, perhaps unorthodox bond with Naruto during this process. Another character could be Neji. He has always been somewhat of a rival and friend to Naruto. Here, he could be the one who is determined to bring Naruto back to his normal self, and a yaoi - themed relationship could potentially develop between them as Neji delves deeper into Naruto's situation.
In such a fanfiction, one possible plot could be that Naruto is exposed to some dark magic or a powerful curse that gradually erodes his humanity. This might lead to him becoming cold and detached from his friends. He could start making decisions that go against his normal moral code, perhaps being more ruthless in battle or in his relationships. The yaoi aspect might come into play if another male character tries to bring back his humanity through a deep emotional and physical connection with Naruto.
A new and mysterious dark ninja could be the main antagonist. This character might have a special ability to corrupt others. They target Naruto specifically because of his power and influence. By using some form of dark jutsu or psychological manipulation, they make Naruto lose his humanity, turning him into a weapon against the very people he used to protect.
Obviously Naruto himself is the central character since the story is about him losing his memories. Sakura would likely be involved too. She's one of Naruto's closest friends and a medic - ninja, so she might try to find a way to restore his memories.
There might be characters from Iwa who oppose Naruto. For example, the Tsuchikage of Iwa would surely be involved as the leader of the village Naruto is attacking.
Iruka - sensei could be one of those who help Naruto. He has always been like a father figure to Naruto and would offer emotional support. Rock Lee could also be a great helper. Lee, who has trained his body to be extremely powerful, could teach Naruto some physical combat techniques that don't rely on eyesight. And of course, the Nine - Tails inside Naruto might also play a role. It could potentially share some of its power or knowledge to help Naruto deal with his new situation.
Sasuke could be one of the main characters. Since Sasuke and Naruto have a complex relationship in the original Naruto series, in a yaoi - inspired fanfiction, he could play an important role when Naruto drops the act.
Another character could be Kakashi. As Naruto's former teacher, he has a lot of wisdom. When Naruto tells him about the future he's seen, Kakashi could offer strategic advice on how to prevent the negative events from occurring. He could also help Naruto understand the possible consequences of their actions to change the future.
Sasuke is often involved. Since Naruto and Sasuke have such a complex relationship, in this 'beyond godlike' scenario, Sasuke might be either a rival trying to match Naruto's new powers or an ally helping him control or use them. Another common character is Kakashi. He could be Naruto's mentor in understanding and managing these extreme powers.
Sakura could be involved. She could be like a healer or an advisor in the new world. Her medical skills would be very useful. Also, Sasuke might be there. He could be a sort of enforcer, using his Sharingan to detect threats. In the world of Asgore, they could form a new kind of team, with Naruto as the leader like Asgore. And then there could be characters from Asgore's world like Toriel. She could be a guide to Naruto about the culture and history of the place.
Hinata would also be very involved. She has deep feelings for Naruto. She might be at his bedside in the hospital, praying for his recovery. After his death, she would be heartbroken and might have to find a new purpose in life without Naruto.