It could also be due to his ongoing feud with a powerful figure in Gryffindor. If this person has enough influence, they could manipulate the situation to get Harry expelled. For example, if a popular Gryffindor student doesn't like Harry and spreads false rumors about him causing trouble in the house, it might 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.
Perhaps there's a misunderstanding. Maybe someone frames Harry for something he didn't do, like stealing important magical artifacts from the Gryffindor common room. The evidence could be so strong against him that the Gryffindor authorities feel they have no choice but to kick him out.
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, 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.
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.
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.
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.
If Harry was kicked out of Gryffindor in Ginny - related fanfiction, Ginny would likely be one of the first to oppose the decision. She might secretly help Harry by providing him with a place to stay in Gryffindor's common room undetected. And she could start her own investigation into what really happened, suspecting foul play. After all, Harry has been a hero in Gryffindor and Ginny wouldn't let him be cast out so easily.
He might seek refuge in another house. For example, he could try to convince the Hufflepuffs to take him in. The Hufflepuffs, known for their acceptance, might be his best bet. This could lead to a whole new set of relationships and storylines as he adjusts to a different house environment.
He might become more independent. Without the support of Gryffindor, he would have to rely on himself more. He could also become more cynical. Being kicked out of his house would be a big blow to his sense of belonging.
In some fanfictions, Gryffindor might kick out Harry Potter due to false accusations. Maybe someone spread rumors that he was using dark magic or endangering the other students. It could also be a plot device to create a more complex and different storyline from the original, where Harry has to fight to prove his innocence and regain his place in Gryffindor.
Maybe it's to fit certain moral or ethical standards set by the fanfiction community. For example, some interpretations of Harry's character might be considered too dark or out of character, so they censor it to keep the overall tone positive and in line with the general perception of Gryffindor values.