Obviously, Harry's closest friends like Hermione and Ron. They would be devastated. Hermione would probably be racked with guilt for not being able to prevent it. Ron would be angry and at the same time lost without his best friend.
The other students at Hogwarts would also be affected. For example, Neville, who looks up to Harry. If Harry ignores everyone, Neville might feel lost. Ginny, who has a special connection with Harry, would be deeply hurt. And the teachers like Snape, who has a complex relationship with Harry, would also be impacted. Snape might be secretly glad at first, but then realize that Harry's isolation could be a sign of a bigger problem in the wizarding world.
The Death Eaters themselves would be affected in an interesting way. Some might welcome Harry with open arms, but others might be suspicious of his sudden change of sides. They might fear that it's a trick by the Order. And within Hogwarts, the students would be in turmoil. Those who idolized Harry would be heartbroken and confused, and there could be a split among the student body depending on who believes Harry's new stance.
Family members, if he has any in the fanfiction world, would be devastated. His mother, for instance, would have to deal with the loss of her son. She might become more involved in the affairs of the demigod world, trying to make sure that her son's sacrifice was not in vain. Also, his half - siblings, if any, would be affected. They could be inspired to step up and prove themselves worthy of Percy's sacrifice.
Peter Parker would be extremely affected too. Iron Man was like a mentor to him. His death could make Peter question his own abilities and whether he can continue to be a hero without Iron Man's guidance. He might also feel a sense of guilt, thinking that if he had been stronger or more experienced, he could have saved Iron Man.
Bella, obviously. She is the one who is pregnant and will have to face all the physical and emotional changes that come with it. Her life will be completely turned around as she prepares to be a mother.
Twilight Sparkle would likely be affected as she is often at the center of things in the MLP universe. Her actions and decisions would be crucial in any alternate ending, whether she's saving the day or facing new challenges.
Sasuke's relationship with Sarada could also be affected. If Sarada experiences things in the past related to Sasuke's family or his past actions, it could make her understand her father better. Maybe she'll come back with a new understanding and they'll have a more open relationship.
Obviously, Harry would be the main character. Since it's about him being a Saiyan. And I think some of his friends from the Harry Potter series might also be important characters, like Hermione and Ron. They could react to Harry's new Saiyan identity in different ways.
Obviously, Harry would be the main character as the title implies. But other characters like Hermione and Ron would also be important. They could either be part of Harry's regime, reluctantly or wholeheartedly, or they could be part of the resistance against his dictatorship.
Obviously, Harry would be the main character. Since it's about him being a playboy, he would be at the center of the story. There might also be his friends like Ron and Hermione. They could play important roles in either supporting or trying to change Harry's playboy ways.