One idea could be Naruto finding himself in the Young Justice universe and teaming up with Artemis. Maybe they go on a mission to stop a new villain who has the power to manipulate time. Naruto's unique jutsu could be a great asset in combat against this villain.
Another plot could involve Artemis getting lost in a dimension similar to Naruto's world. Naruto then helps her find her way back while also protecting her from the various threats in his world, like rogue ninjas. They could learn from each other's combat styles during this adventure.
Maybe Artemis's sister is an undercover agent in an enemy organization. She has to balance her loyalty to her sister and her mission. She could send coded messages to Artemis, and Artemis has to figure out what they mean. This would add a lot of mystery and tension to the fanfiction.
One idea could be that Robin and Artemis are on a solo mission together and get trapped in a strange, magical place. As they try to find a way out, their feelings for each other intensify. Another could be a post - battle scenario where they're both injured and have to rely on each other for care, leading to some romantic moments. Or perhaps a time - travel plot where they see alternate versions of themselves in different relationships and it makes them realize their feelings for one another.
Maybe a story where Icicle Jr has a change of heart and tries to defect from his villainous group. Artemis is initially skeptical but decides to help him. Along the way, they have to evade capture from both the villains and some overzealous heroes who don't trust Icicle Jr's intentions. This could lead to some intense action scenes and character development for both of them.
One idea could be that Naruto is somehow transported to the Young Justice universe. He then has to learn how to work with the team while also dealing with villains he's never faced before. Another plot could be that a villain uses some sort of magic or technology to merge the two worlds, forcing Naruto and the Young Justice members to cooperate to separate them again.
A more complex plot could be that there is a prophecy in both universes that foretells of a combined force from both Naruto's world and the Young Justice world being the only thing that can stop an upcoming great evil. This would lead to a series of events where characters from both sides have to learn to trust and work together. Naruto could bring his friends from Konoha, and together with the Young Justice team, they would train and strategize to face this ultimate threat.
A good plot idea might involve Artemis getting kidnapped. Green Arrow then has to track her down, using all his skills and resources. Along the way, he discovers some secrets about Artemis' past that she has been hiding from him. Or perhaps a plot where they are both framed for a crime they didn't commit. They have to work together to clear their names, while also dealing with other superheroes who think they are guilty.
One idea could be a crossover where the Young Justice team has to team up with the Justice League to face an interdimensional threat. Maybe a powerful villain from another dimension is trying to invade Earth and the combined skills and powers of both groups are needed to stop it.
Maybe a story where some of the younger members of the Young Justice team are frustrated with the Justice League's methods and decide to take on a mission on their own, but end up getting in over their heads and have to call in the League for help. This could lead to a lot of character development and some interesting dynamics between the two groups.
One plot idea could be that they are undercover on a mission as a couple. As they get into character, they end up having a real moment and kiss. This kiss then makes them question their true feelings for each other.
One idea could be that the Young Justice team gets accidentally transported to an alternate dimension where the Justice League has turned evil. The Young Justice members then have to figure out how to reverse the situation while also evading capture from their once - heroes. Another could be a time - travel plot where the Young Justice team travels back in time and teams up with the early days of the Justice League to stop a threat that was thought to be long gone but has resurfaced in their own time. A third idea is that a powerful new villain emerges who can only be defeated by a combined effort of the Young Justice and Justice League, but first they have to overcome their differences in fighting styles and leadership.