Not exactly. Batman Begins is one interpretation of Batman's origin story, but it's not the definitive or only 'real' one. Different Batman stories and adaptations offer various takes.
Yes, Batman Begins can be considered a mystery fiction to some extent. It has elements of mystery as Bruce Wayne uncovers secrets and faces hidden threats in Gotham City.
One interesting aspect could be the different perspectives it offers on the well - known Harry Potter story. Fanfics often explore characters in new ways or develop alternative plotlines that the original might not have touched upon. For example, they might focus on a minor character's backstory in more detail.
One idea could be that Batman, in his quest to fight crime in Gotham, discovers some sort of interdimensional rift that leads him to the world of The Avengers. He then has to team up with them to stop a common enemy that is using technology from both universes to cause chaos. For example, Loki could be teaming up with some of Batman's rogues gallery like The Riddler to create complex puzzles and illusions that are both magical and technological in nature.
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.
It probably points out how the plot is fragmented. There are different stories that seem unconnected at first but are actually intertwined. For example, the story of the briefcase is a thread that runs through different parts of the movie.