Another plot could involve them going on adventures together outside of their superhero duties. For example, they could explore some ancient ruins and discover a new threat that they have to face as a couple. In these fanfictions, there could also be some jealousy from other characters who might have feelings for either Batman or Wonder Woman.
A possible plot is that they initially clash because of their different approaches to justice. Batman is more brooding and operates in the shadows, while Wonder Woman is more open and idealistic. But through their relationship, they learn from each other and find a new way to fight for justice together.
In a kids' fanfiction scenario, Batman and Wonder Woman could be transported to a world of toys. They would be shrunk down to the size of toys themselves. There, they meet a group of toys who are in danger of being thrown away. Batman and Wonder Woman then have to find a way to convince the kids who own the toys to keep them. They might go through a series of comical and heartwarming events to achieve this goal. It would be a story that emphasizes the value of things and the importance of taking care of them.
One possible plot could be that Wonder Woman is under the influence of some sort of mind - control. Maybe a villain has taken over her mind, and she attacks Batman, who is initially confused as to why his ally has turned on him. Another plot could be a difference in their views on how to handle a major threat in Gotham or the DC universe as a whole. Their conflicting approaches lead to a physical altercation where Wonder Woman accidentally hurts Batman.
Well, it could start with a gala event where all the superheroes are present. Batman and Wonder Woman are paired for a dance, and there's an instant spark. They decide to go on a proper date. Their date might be a flight together over the city, with Wonder Woman carrying Batman. As they date, they start to influence each other. Batman becomes a bit more open and less brooding, while Wonder Woman learns some of Batman's detective skills. But then, they have to deal with public opinion within the superhero community, some of whom think they should focus only on their duties.
Another great fanfiction could be a time - travel story. Wonder Woman and Batman get sent back in time to an era they know little about. They have to rely on each other's skills and adapt quickly to survive and find a way back to their own time.
Maybe in a fanfiction, they kiss during a moment of extreme danger. For example, Batman is about to sacrifice himself to save Wonder Woman and she stops him with a passionate kiss. This could be the start of a new relationship dynamic where they start to question their previous boundaries and how they feel about each other.
One interesting storyline could be Batman and Wonder Woman teaming up to take on a new, powerful villain that neither could face alone. This villain could be a magical threat that requires Wonder Woman's knowledge of the mystical and Batman's strategic mind.
One interesting storyline could be the two superheroes uniting to fight a new, powerful villain that threatens both Gotham and Themyscira. Their marriage would symbolize the union of two different worlds, and they'd use their combined skills and resources to protect everything they hold dear.
One interesting storyline could be their child having to hide their powers in a normal school. They'd struggle to fit in while also having the responsibility of their superhero heritage. Another could be the child getting kidnapped by a villain who wants to use their unique genetic makeup for evil.
One interesting storyline could be the son's struggle to balance the very different legacies of his parents. He might have Batman's brooding nature and tactical mind, while also having Wonder Woman's sense of justice and connection to the gods. This internal conflict could lead to some great character development.
A great plot could be a love story between them in the fanfiction world. They come from different backgrounds, she's an Amazonian princess and he's a brooding vigilante from Gotham. Their relationship could be filled with misunderstandings at first but then develop into a deep connection. For example, they might initially clash over their different approaches to justice but later find common ground and fall in love.