How would other characters react in a fanfic if Harry leaves the Potter family?

Well, Ginny would be heartbroken that Harry left. She might have expected to build a life with him after Voldemort was defeated. But she's also a strong character, so she would likely throw herself into her own life, perhaps becoming a star Quidditch player. Neville would be overjoyed that Voldemort was dead. He might take on a role at Hogwarts, teaching herbology perhaps, and sharing his knowledge with the students. As for the other characters in the wizarding world, those who had suffered under Voldemort would be in a state of jubilation and start to pick up the pieces of their lives.

Hermione would probably be both amused and concerned. She might try to find a magical solution to get him out of this situation as quickly as possible while also having a bit of a chuckle at the absurdity of it all.

The other students at Hogwarts would be very afraid. Some might avoid Harry out of fear that Voldemort could use him to harm them. But Neville, being brave, would probably try to reach out to Harry in some way, believing that there's still good in him. The Order of the Phoenix would be in chaos at first. But then they'd start formulating plans. Lupin would be worried but also think rationally about how to deal with the situation, using his experience as a werewolf and a wizard.

Sasuke might be conflicted. He has his own complex relationship with Naruto. Part of him might understand Naruto's reasons for leaving, but he could also be angry that Naruto didn't confide in him. Sakura would be worried sick. She has always cared about Naruto, and his leaving would leave a big hole in the team. Kakashi, on the other hand, would be disappointed but also respect Naruto's decision if he thought it was for a noble cause.

The Weasley family would have a range of reactions. Mrs. Weasley would probably be very maternal towards Harry, seeing Lily in his face. Ginny might be a bit shy around Harry at first, seeing him in a new light. Fred and George would likely use it for some good - natured teasing, like creating potions that make Harry's hair grow really long to enhance the resemblance. And Snape, well, seeing Harry look like Lily would be a constant reminder of his unrequited love. He might be even more conflicted in his feelings towards Harry, part of him hating Harry for being James' son but also being drawn to him because of his likeness to Lily.

Well, Harry Potter is a rather humble character. He might initially feel a bit embarrassed to see himself as the center of so many fictional stories created by fans. If the fanfic portrays him as a hero in new adventures, he would probably be honored. However, if it misrepresents his friends or the values he holds dear, he could be a bit indignant. He would likely approach it with an open mind but also with a sense of protectiveness towards his own story and those he loves.

The characters close to Rias might be relieved. If they see Naruto as an outsider or a potential threat, his leaving would be a good thing for them. They would probably go back to their normal routines without Naruto's presence causing any disruptions. For example, some of Rias's devil comrades who are more traditional might not like Naruto's different ways and values.

Ginny would likely be heartbroken. She's a strong character but she loves Harry deeply. She might start to question herself and what she did wrong. Cho, on the other hand, would be surprised but also happy. She may have still had feelings for Harry all along. Harry himself would be conflicted at first, feeling guilty for leaving Ginny but also excited about the possibility with Cho.

Ron would be extremely angry at first. He might feel betrayed by Harry. But as he realizes that something must be seriously wrong with Harry, he would probably join Hermione in trying to save Harry from Voldemort's influence. They would look for a way to break whatever spell or false belief has hold of Harry.

Dumbledore would likely view it as another sign of Harry's individuality. He would see it as Harry growing up and making his own choices, as long as it doesn't interfere with his destiny. Snape might sneer at it, thinking it's just another Gryffindor folly. But secretly, he might respect Harry's courage to do something different.