A citizen who has witnessed the Joker's crimes up close and personal multiple times. This could be someone who lives in a neighborhood that the Joker frequently targets. Over time, they become fed up with the fear and chaos and decide that they are the only one who can put an end to it. They might not have any special skills, but their determination is enough to drive them to kill the Joker.
Maybe a family member of a police officer killed by the Joker. This civilian has a strong sense of justice and a personal vendetta. They are not bound by the same rules as the police and are more likely to take extreme measures. They have seen the destruction the Joker has caused to their family and will stop at nothing to get revenge.
One possible plot could be that the civilian has lost someone dear to the Joker's actions and decides to take revenge. For example, if the Joker killed the civilian's family member in a heinous crime, the civilian might spend months planning and training in secret to finally confront and kill the Joker. Another plot could be that the civilian is a vigilante who has had enough of the Joker's chaos in the city and decides to take matters into their own hands to protect the city.
Batman's allies are very likely. For example, Robin. The Joker would see kidnapping Robin as a great way to taunt Batman. Also, Commissioner Gordon might be a target as he represents law and order, which the Joker loves to disrupt.
In some fanfiction scenarios where Naruto kills the civilian council, it might be seen as a reaction to years of mistreatment and oppression. The civilian council in the Naruto universe has often been shown to be short - sighted and discriminatory towards Naruto. However, from a moral standpoint in the real world, killing is never an easy solution. But in the context of a fictional and often corrupt world of Naruto fanfiction, it could be a way to show Naruto breaking free from the chains that have held him back for so long.
Well, it could start with the Joker causing mayhem in a village in Naruto's world. Naruto, being the hero, tries to reason with the Joker at first. But when he realizes the Joker is beyond reasoning, he uses his ninjutsu skills. He might start with some basic fire - style jutsu to test the Joker's limits and then progress to more powerful attacks like his Nine - Tails Chakra Mode attacks until the Joker is defeated.
Well, it could be that Naruto, with his ninja skills, sees the Joker causing chaos in his world which has somehow merged with the DC universe. He might use his Rasengan to take down the Joker. Maybe the Joker has a new evil plan involving stealing chakra or something, and Naruto just won't stand for it.
Well, in a fanfiction world, anything can be possible. Maybe Harry Potter uses his magic skills like the Killing Curse. But it's really a strange crossover. The Joker is from a completely different universe with no magic, and Harry Potter is from a world full of magic. It would be a very unique and perhaps disturbing story to see how Harry Potter overcomes the Joker's chaos and madness with his magic and finally kills him.
It's a really wild idea. On one hand, Naruto has the power to take on the Joker. His chakra abilities like the Rasengan could potentially be a deadly weapon against the Joker. But on the other hand, the Joker is a master of psychological warfare, which Naruto may not be used to dealing with. In a fanfiction, it would be fascinating to see how the writer would make these two characters interact and how Naruto would ultimately defeat the Joker.
Well, one possibility could be that Naruto's powerful ninjutsu skills give him an edge. He might use his Shadow Clone Jutsu to confuse the Joker and then land a fatal blow with a Rasengan. Another aspect could be Naruto's strong sense of justice which drives him to take out the chaotic Joker in the Justice League universe.
Well, one possibility is that Naruto, tired of the shinobi life, decides to give it all up. He might start a simple life in Konoha as a civilian, perhaps opening a ramen shop like his favorite place. He'd interact with the villagers in a new way, no longer as a ninja but as an ordinary person, and face new challenges like managing a business and dealing with local politics in a civilian context.
Batman would definitely be a main character. He's the Joker's arch - nemesis, and when the Joker becomes a baby, Batman might be the one who first discovers him. He'd be in a moral dilemma about what to do with this baby version of his greatest enemy.