The Flash might initially be in denial. He's used to Batman always having a plan and his death would be a huge shock. He would then turn his speed into a tool for investigation, trying to find out exactly what happened. Green Lantern could feel a sense of loss but also be spurred into action, using his ring to try and prevent future tragedies like Batman's death. He might create constructs in Batman's memory to inspire the team.
One possible plot could be that Naruto somehow gets transported to the DC universe where the Ace Justice League exists. He could initially be seen as a threat due to his strange powers. But as they get to know him, they realize his good intentions. Naruto could teach the League some of his ninja techniques, like how to use chakra to enhance their physical abilities. And in return, the League could introduce Naruto to advanced technology and different ways of justice in their world.
Well, in a fanfiction, anything can be possible. Naruto's skills like his shadow clones and Rasengan could potentially be used to rescue Ace. Maybe he uses his speed to get through the Justice League's defenses, which are set up around Ace for some reason. And then he uses his clones to create a distraction while he frees Ace with his combat abilities.
The plot in a 'Justice League Unlimited Oc Fanfic' can be really diverse. It might introduce new characters (OCs) with unique powers and backstories. These OCs could interact with the existing Justice League members in various ways. For example, an OC with telepathic abilities might help the League in a battle against a mind - controlling villain. The fanfic could also explore different relationships among the characters, both old and new. It might show how the OCs adapt to the world of the Justice League and how they are received by the established heroes.
In 'justice league unlimited oc fanfiction', the theme of identity crisis is often seen. The OCs are new characters in an established universe, so they struggle with their identity. Another theme is the struggle against prejudice. Since they are original characters, sometimes the other superheroes in the Justice League are prejudiced against them at first. And the theme of growth is also prevalent as the OCs develop their skills and personalities throughout the story.
In my opinion, the most memorable characters in a 'Justice League Unlimited Oc Fanfic' are often those that have complex backstories. For example, an OC who was once a villain but turned good. Their internal struggle between their former evil ways and their new - found heroism is fascinating to read. Also, an OC with the power of invisibility who uses it not just for sneaking around but also to understand the other characters better without being noticed can be quite memorable.
The plot could start with Ace being in trouble in the Justice League's world. Maybe he's been captured by an enemy of the League. Naruto somehow gets wind of this and decides to help. He travels to the Justice League's realm and starts his search for Ace. Along the way, he meets some of the Justice League members who are initially skeptical of him but then see his potential. Together, they find Ace and Naruto uses his jutsu to defeat the bad guys and free Ace.
Another possibility is Flash and Naruto. Flash, with his super - speed, would be one of the first to reach Naruto if he suddenly appears in the DC world. Flash's friendly and curious nature would lead him to start a conversation with Naruto right away. Naruto would be amazed by Flash's speed and might try to compete with him in some way, which could be the start of their interaction.
The most interesting element is the power mash - up. Naruto characters have chakra - based powers like jutsus, and Justice League members have superpowers. Combining these, like seeing Flash race against Naruto in his super - speed mode, is really exciting. Also, the clash of ideologies. The concept of justice in the Justice League and the shinobi way in Naruto can lead to great character debates and development in fanfictions.
Power - how Naruto's ninja powers compare and contrast with the superpowers of the Justice League members. For example, Naruto's Rasengan vs Superman's heat vision. This theme of power comparison and how they can work together is often explored in these fan fictions. Another theme is friendship. Just like in the Naruto series, friendship plays a big role. Naruto might form strong bonds with the Justice League members and they all work together to overcome challenges.