Harry is the central figure for sure. But there could be new characters created specifically for this fanfiction. Maybe a guide in the realm of Death who helps Harry understand the rules of the deal. Or a character who has already made a deal with Death and can give Harry some advice. And of course, Dumbledore's spirit could also appear to offer some wisdom to Harry regarding his deal with Death.
Well, aside from Harry and Death, his friends like Hermione and Ron could also be important characters. They might try to stop Harry from making the deal or help him fulfill the terms of the deal. There could also be some other magical creatures or beings that are associated with Death, such as the Grim Reaper - like figures in the wizarding world. And perhaps some powerful wizards or witches who have had past experiences with Death could also be part of the story.
Obviously Naruto and Kyuubi are the main characters. Naruto is the one making the deal, and Kyuubi is the one with whom the deal is being made.
Obviously, Harry Potter would be the main character since it's in his name. He is the one who befriends Death. Hermione Granger and Ron Weasley are also likely to be important characters. They are Harry's closest friends and would be involved in the story, either trying to understand Harry's new friendship with Death or being affected by it in some way. For example, they might be worried about Harry's sanity or the implications of befriending such an otherworldly being.
Obviously, Harry Potter himself. He's the one who has become the Master of Death. Hermione and Ron would also be important. They'd be there to support Harry, and also to question his new power and the moral implications. Dumbledore might also play a role, perhaps as a guide from beyond the grave, since he was always so interested in the Deathly Hallows and what it means to be the Master of Death.
Obviously, Harry Potter himself would be a main character since the title revolves around him. Hermione and Ron are also very likely to be involved. They are Harry's closest friends throughout the series and would surely play a part in a story where Harry is welcoming death. They might try to stop him or support him depending on the direction of the fanfiction.
There could be an antagonist in the fanfic. Maybe someone who had a vendetta against Harry Merchant and was somehow involved in his death. This character would add conflict to the story as the people left behind try to figure out what really happened to Harry.
Neville Longbottom could also play a more prominent role. Neville has his own growth arc in the series, and after Sirius's death, he could bond more with Harry over their shared experiences of loss. They could support each other in their fight against the Dark Arts. And perhaps some of the Death Eaters who were involved in Sirius's death could be main characters from the antagonist side, as Harry tries to track them down and bring them to justice.
Voldemort would remain a major character. Harry's new abilities and perspective from being raised by Death would make their conflict even more complex. Harry might approach the fight against Voldemort with a different strategy, one that is influenced by the teachings of Death.
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.
Well, Harry Potter is the key figure. In the harem, there could be characters like Daphne Greengrass. She is from a pure - blood family and could bring an interesting perspective. Pansy Parkinson could also be a part of it, which would create a lot of drama considering her previous attitude towards Harry. And then there's Tonks, who is a fun and unique character and could be an interesting addition to the harem.
Well, it could be that Harry makes a deal to sacrifice himself to save his friends. Maybe he agrees to let Death take him at a certain time in exchange for their safety.