The Scooby Gang as a whole would be severely affected. They were a tight - knit group led by Buffy. Without her, they'd have to re - evaluate their roles and dynamics. They might argue about how to move forward, with some wanting to continue in Buffy's footsteps and others being too grief - stricken to think about fighting evil. This would create a lot of tension and character development within the fanfic.
Sasuke would be one of the most affected. He and Naruto had a complex relationship, from being rivals to friends. Naruto's death would leave a huge void in Sasuke's life. Also, Hinata. She loves Naruto deeply, and losing him would be devastating for her.
Perhaps the fanfic could be a more spiritual take on Buffy's funeral. It could explore different religious or supernatural beliefs within the Buffyverse. For example, there could be a ceremony that combines elements of witchcraft and traditional mourning. Buffy's friends might perform a ritual to send her spirit to a peaceful afterlife, while also dealing with their own grief and guilt for not being able to save her.
Obviously, his closest friends Hermione and Ron would be very important. They were with him through so many things. Hermione would likely be the one to organize and ensure everything was done properly. Ron would be there for emotional support to Hermione and to share his own grief.
Definitely the Bat - family. Robin, Nightwing, Batgirl, etc. would be there to pay their respects. Alfred, who has been like a father figure to Batman, would also be present. And of course, Commissioner Gordon, as he has been Batman's ally in the fight against crime in Gotham for a long time.
For Buffy, her friends like Willow and Xander would be likely allies. Willow could use her magic to give Buffy an edge in any magical challenges, and Xander would be there for moral support and to offer his own brand of scrappy help. Giles, too, with his vast knowledge of the supernatural.
Definitely Sakura. In the original story, she is often in Naruto's circle. With Naruto's chakra - absorbing ability, she might find herself in more dangerous situations as Naruto could attract stronger enemies. Also, Jiraiya. He was Naruto's mentor in many ways. Now, he would have to guide Naruto in a different way to ensure he doesn't misuse this power. And Pain would be highly affected too. Pain's plan to collect tailed - beast chakra could be thwarted by Naruto's new ability to absorb chakra, which would completely change the Akatsuki's plans and thus the overall plot.
I think Sango would also be greatly affected. As a female in the group, she might feel a stronger sense of responsibility towards baby Kagome. She would be worried about how to take care of her properly, especially in their rather dangerous world full of demons. And she might also be concerned about how this would impact their overall mission and group dynamic.
I think Naruto would be one of the most affected. Since he and Hinata have a special connection, having her turn into a baby would completely change their dynamic. He'd have to step up and be responsible in a new way.
Lucy would be very affected. She's one of Natsu's closest friends. She'd have to take on a lot of responsibility for taking care of baby Natsu, which would disrupt her normal life of doing quests and writing her novel.
Hinata would also be highly affected. She has always admired Naruto from afar. By seeing his memories, she would understand him on a whole new level, his struggles, his hopes, and it would likely strengthen her feelings for him even more. And it could also change how she interacts with him in the story.