One possible reason could be a serious rule violation. For example, if Harry was wrongly accused of using dark magic within the Gryffindor common room. Another reason might be that he was framed for stealing the Gryffindor sword. It could also be due to a conflict with other Gryffindor students that got out of hand and the house decided they couldn't keep him anymore.
Well, in some fanfictions, it could be because of a prophecy that the Gryffindor house leaders misinterpreted. They might think that Harry's presence would bring great danger to the other students in Gryffindor. Or perhaps Harry's connection to Voldemort was seen as too much of a liability for the house. Say, if there were some dark magic related incidents and Harry was suspected because of his link to Voldemort, even if he was innocent.
Maybe he's falsely accused of stealing important Gryffindor artifacts. For instance, if the Sword of Gryffindor goes missing and Harry is wrongly blamed, the house might decide to kick him out. It could be part of a plot by a jealous student or an outside force trying to disrupt Hogwarts.
It could be due to a series of bad decisions that made him seem like a bad influence in Gryffindor. For example, if he constantly got into fights with other Gryffindors and disrupted the harmony of the house, they might kick him out. Also, if he was caught breaking too many school rules in a way that reflected poorly on Gryffindor as a whole, like sneaking out at night to go to the Forbidden Forest too often without a good reason, that could lead to his expulsion.
One reason could be that he breaks a major school rule. For example, if he uses dark magic without proper authorization, the Gryffindor house might decide to expel him. Gryffindor values courage, but there are limits, and using dark magic goes against the values of the school as a whole.
One possible reason could be his unruly behavior. Naruto is known to be a bit of a troublemaker in the series, always pulling pranks. In fanfiction, this might be exaggerated, and the orphanage might not be able to handle it anymore. Another reason could be that he's suspected of being involved in something dangerous or illegal, even if he's innocent. For example, if there are strange incidents around the orphanage and Naruto is the easy target to blame because of his reputation.
One possible reason could be his prankster nature. Maybe he played one too many harmless but annoying pranks on the staff or other orphans, and they decided they'd had enough. Another reason might be the fear of the Nine - Tails within him. Even if the people in the orphanage didn't fully understand what it was, they could sense something dangerous about Naruto and wanted to distance themselves from him for safety reasons.
It could also be due to a false accusation. Perhaps someone framed him for something he didn't do, like stealing important artifacts from the school. And in the world of RWBY, if he was found to be secretly associated with a group that the school considered dangerous, that would also lead to his expulsion.
Ginny could first be in shock. But then, she would start thinking of ways to help Harry. She could offer him emotional support, like being there for him when he is feeling down about being expelled. She may also try to rally their mutual friends to support Harry, whether it's by protesting the decision or by helping him find a new place to belong in the school.
In some fanfictions, it could be a political move within Hogwarts. There might be a group that wants to undermine Dumbledore's influence, and since Harry is so closely associated with him, they target Harry by getting him banished from Gryffindor. This could also be related to the discovery of some long - hidden secret about Harry's family that makes the Gryffindors view him differently.
Another reason could be related to a new prophecy. Suppose a new prophecy emerged that said Harry Potter's presence in Gryffindor would bring great danger to the house. The Gryffindor students and faculty, believing in the importance of protecting the whole house, might have decided to banish him. But of course, this would be a very difficult decision as Harry has been an important part of Gryffindor before. And in the end, the prophecy might turn out to be misinterpreted.
In some fanfictions, if Harry is kicked out of Gryffindor, he might end up joining another house like Hufflepuff. The Hufflepuffs are known for their acceptance and might welcome Harry with open arms. This could lead to a whole new set of adventures for Harry, as he would have to adjust to the different values and culture of Hufflepuff house.