Another possibility is that Bruce is making moral decisions in the fanfic that Alfred doesn't agree with. As Alfred has his own set of values and he has been around Bruce for a long time, if Bruce starts to cross certain ethical lines in the name of justice, Alfred would be disappointed.
One reason could be that Bruce Wayne never had the traumatic event that led him to become Batman in the original story. Maybe his parents' death was prevented somehow, so he never felt the need for vengeance and justice in that extreme way.
In many fanfics, Harley Quinn realizing Bruce is Batman can lead to some really interesting plot developments. Maybe she discovers it by accident, like seeing Bruce act in a way that's too similar to Batman's mannerisms. It could also be that she pieces it together from some clues that others have overlooked. This realization might make her re - evaluate her relationship with both Bruce and Batman, and it could create a whole new dynamic in the story.
One interesting aspect of Batman and Bruce Banner fanfiction could be a scenario where they team up. Batman, with his detective skills and martial arts prowess, could work alongside Bruce Banner, who has the incredible strength of the Hulk at his disposal. Maybe they'd face a common enemy that requires both brains and brawn, like a super - intelligent villain who also has a powerful army. This would make for an exciting story as they combine their unique abilities to save the day.
In Batman and Bruce Banner fanfiction, there could be a plot where they first start as enemies. Batman might see the Hulk as a dangerous uncontrollable force, while Banner might see Batman as a self - appointed judge. But as the story progresses, they realize they have more in common than they thought. They both have a dark side to them, Batman with his brooding nature and Banner with his inner struggle against the Hulk. Their journey from enmity to alliance could be a great story.
One reason could be Bruce's increasing isolation. Alfred sees Bruce pushing away friends and allies in the fanfic. This makes Alfred disappointed because he knows that Batman needs a support system. Without it, Bruce is more likely to burn out or make hasty decisions that could have been avoided with some input from others.
Maybe Alfred is disappointed because Bruce in the fanfic makes some unwise decisions as Batman. For example, he might take excessive risks that could endanger his life or the safety of Gotham in a way that goes against Alfred's advice.
Well, in such a fanfic, it might show Bruce Wayne as a completely different entity from Batman. Maybe Bruce is just a normal rich guy who has no idea about the vigilante activities of Batman. He could be living his own life, focused on business and social events, while Batman is someone else entirely, perhaps an unknown figure with no connection to the Wayne family.
One idea could be that the OC is a childhood friend of Bruce's who has a unique skill, like being an expert in ancient martial arts from a far - off land. They could influence Bruce's training and view on justice in a different way. For example, they might introduce him to more spiritual aspects of combat and self - discovery.
One possible reason could be that Bruce is being too reckless in his Batman activities. Alfred, being the caretaker, might see Bruce endangering himself unnecessarily and decides to punish him to make him more cautious.