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 possible fanfiction could be about Bruce's daughter growing up in the shadow of her father's legacy. She might struggle with the expectations placed on her and try to carve out her own identity. For example, she could have a different approach to fighting crime, perhaps focusing more on prevention through community work rather than donning a costume like Batman.
She could be a source of emotional support for Bruce. In the movie, Bruce is often alone in his journey, but with a sister, she could be there to comfort him during the tough times, like after his parents' death.
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.
Batman Begins tells the origin story of Bruce Wayne. He witnessed the murder of his parents as a child, which deeply traumatized him. This event led him on a journey to fight crime. He trained with the League of Shadows, learning various combat and stealth skills. But he ultimately rejected their extreme methods. Returning to Gotham, he used his family's wealth and resources to create his Batman persona, with the intention of cleaning up the crime - ridden city.