In a more complex plotline, Batman might be tricked into a situation where his death is the only way to stop a large - scale destruction. He might have to make a deal with a villain that costs him his life. Wonder Woman then has to deal with the guilt of not being able to save him as well as the responsibility of taking over some of his duties in protecting Gotham and the world. She may also start to investigate the circumstances around his death more closely and discover secrets that Batman was keeping.
Perhaps Batman is caught in a cross - fire between two super - powerful forces while trying to protect Wonder Woman. He endures fatal injuries but still manages to give Wonder Woman the motivation to fight on and keep the world safe. It could also be that he makes a miscalculation in a battle plan and pays the ultimate price, which then makes Wonder Woman question her own abilities and push herself to be better in his memory.
One possible plotline could be that Batman sacrifices himself to save Wonder Woman from a powerful enemy. Maybe he takes on a self - destructing device or holds off a horde of villains while she escapes. Another could be that he is poisoned by a new and deadly toxin, and in his final moments, he imparts some crucial knowledge or advice to Wonder Woman.
She could be devastated. Wonder Woman might go into a period of mourning, isolating herself from others as she grapples with the loss. She was used to having Batman as an ally, and his death would leave a big hole in her life.
One possible storyline could be that they are facing an extremely powerful and ancient evil. This evil has the power to corrupt the very essence of the world. Batman and Wonder Woman, in their attempt to stop it, find themselves in a situation where they have to sacrifice their lives. Maybe they are lured into a trap where the only way to prevent the evil from spreading across the universe is for them to use their combined powers in a self - destructive way.
Maybe it takes place in an alternate universe where the world is a bit different. Batman is more open with his emotions. He takes Wonder Woman to a special place, like an ancient, hidden garden. There, he tells her how much she means to him, not just as a teammate but as someone he has romantic feelings for. He might talk about how her strength and beauty have always attracted him, and how he has been trying to hide these feelings for a long time but can't anymore.
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.
A possible storyline could be that Wonder Woman comes to Gotham to investigate some strange occurrences that seem related to her world. She teams up with Batman, and they discover a cult that is trying to summon an ancient evil. Along the way, they learn to respect each other's methods.
A common plotline could be that Batman gets involved with another female character. Maybe he starts to develop feelings for Catwoman due to their shared history of being on the wrong side of the law sometimes. This new relationship on Batman's part could make Wonder Woman feel betrayed and her heart broken.
One possible plotline could be that Batman confesses his love for Wonder Woman during a dangerous mission. They're in a tight spot, and he realizes he might not get another chance. So he blurts it out, adding a whole new layer of tension to their already complex relationship as superheroes.
One possible plotline could be that Batman and Wonder Woman are forced to work closely together on a mission that spans multiple dimensions. As they face various challenges, they gradually realize their feelings for each other. For example, Batman, who is usually so stoic, starts to open up to Wonder Woman about his past traumas, and she in turn shares her own insecurities about being an Amazon in a man's world.
In some fanfics, like 'The Amazon, the Bat and the Cat', the plotline involves a magical artifact that can only be retrieved by the combined skills of Batman, Wonder Woman and Catwoman. This forces them to cooperate in a way they haven't before, with Wonder Woman using her strength and magic, Batman his detective skills and Catwoman her agility.
Darkseid is another possibility. He's a powerful and menacing villain. If he sets his sights on Wonder Woman, Batman would be forced to act. He'd need to use all of his skills and resources to save her from Darkseid's Omega Beams and his army of minions.