Well, in fanfiction, anything can happen. Just because it says Harry is Uryu's brother doesn't necessarily mean it's going to be a traditional brother relationship. It could be a metaphorical brotherhood, or it could be a result of some crazy plot device like a cross - over between two different universes. So, it really varies from one fanfiction to another.
Well, a Nishimiya x Ishida fanfiction often explores the relationship between these two characters. It could be about their friendship deepening into something more, like a romantic relationship. The fanfiction might focus on their interactions, how they understand each other's feelings, and the development of their bond over time.
I'm pretty sure Ishida doesn't have a niece in the manga. Usually, such significant family relations would be clearly shown or at least hinted at, but there's been no indication of this.
A fanfic with this theme could be really interesting. It might explore a more humorous or unique side of Uryu's character. Maybe it could involve his friends or enemies using tickling in a light - hearted way to get a reaction from him. But again, it depends on the creativity of the fanfic writer.
One great ichigo x uryu fanfic is 'Bond of Souls'. It beautifully explores their relationship as they face a new and powerful enemy together. Their friendship is depicted in a very heartwarming way.
Ishida doesn't die. The manga follows a different trajectory for his character arc, emphasizing his personal development and relationships rather than a tragic end like death.
A common theme is the exploration of Uryu's dual identity as a Quincy and his relationship with the reader. For example, how the reader might react to his Quincy powers and the responsibilities that come with it. Another theme could be friendship turning into love. Maybe they start off as comrades in some sort of battle situation and then gradually develop deeper feelings for each other.
Neliel could be a great choice. She has a more gentle and kind nature compared to many other Arrancars. Her unique appearance and backstory would make for an interesting dynamic with Uryu. She could potentially teach Uryu about the different aspects of Arrancar existence that he may not be aware of.
One key element is their contrasting personalities. Ichigo is hot - headed and impulsive while Uryu is more calm and calculated. This creates an interesting dynamic in the fanfic as they often clash but also learn from each other.