Another option is a group of rogue ninjas. They see Naruto as a threat to their plans of chaos and domination. So, Naruto fakes his death to infiltrate their ranks and stop them from within.
It could be a new, powerful ninja who has a vendetta against Naruto. This antagonist might be jealous of Naruto's popularity and power, and wants to take over the Hidden Leaf Village.
A secret organization that has been operating in the shadows and views Naruto as a major threat to their plans. They might be planning something big like taking over the ninja world, and Naruto's presence and influence stand in their way. So, Naruto fakes his death to gather intelligence on this organization without alerting them.
Another possibility is that the main antagonist is a group. It could be a secret organization that Naruto discovers is plotting something big. Since they are so powerful and well - connected, Naruto fakes his death to infiltrate them and expose their plans from the inside.
It could be the Green Goblin. He's always been a major foe of Spider - Man and might be the reason for Spider - Man to fake his death, like if he's planning a huge attack and Spider - Man needs to deceive him to stop it.
It could be an ancient dark ninja who wants to use Naruto's new 'avatar of death' powers for his own evil purposes. This ninja might have been researching death - related jutsus for years and sees Naruto as the key to his ultimate power.
It could be a rogue ninja from another village who has a long - standing grudge against Naruto. Maybe this ninja has been plotting for years to take revenge on Naruto and when Naruto fakes his death, he starts to target Naruto's friends and family instead, thinking it will draw Naruto out.
Harry is the main one as it's his faked death. Hermione, with her sharp mind, would be a mainstay in the story. Ron, with his loyalty and bravery, would be right there. Neville could also be a main character. He has grown a lot throughout the series and could be involved in the events surrounding Harry's faked death, perhaps even being one of the first to suspect something fishy. And then there's Ginny. As Harry's love interest, she would be deeply affected by his faked death and would be a central figure in the emotional turmoil of the story.
A rival medicine cat from another Clan might be the main antagonist. They could see Alderheart as a threat to their own status or the well - being of their Clan. So they might use dark magic or some underhanded tactics to bring about his death.
A dark and mysterious sorcerer could also be the main antagonist. The sorcerer has a long - standing grudge against Byakuya's family or the place he protects. Using dark magic, the sorcerer sets up a series of deadly traps and curses, which ultimately lead to Byakuya's death.
It could be a new, self - made villain. Maybe a rogue ninja who was once rejected by the Hidden Leaf Village. He blames Naruto for his misfortunes and decides to target his sister as revenge. This villain would have his own set of unique and dangerous jutsu, which Naruto would have to figure out how to counter in order to save his sister.
It could be a new character created specifically for the fanfic. Maybe a rogue ninja from a far - off land who has a vendetta against Naruto. This antagonist might be after Naruto's power or trying to stop him from achieving a certain goal.