First, understand the characters of Nightwing, Batgirl and the Young Justice universe. Read the official comics and watch the shows related to them. Then, come up with an interesting plot, like a new threat they have to face together.
The character of Nightwing is really cool. His acrobatic skills and detective abilities make for exciting stories in the Young Justice setting. Fanfiction writers can explore his relationships with other characters like Superboy or Artemis.
They are popular because they both have a connection to Batman. They share a similar background of being trained by him, which gives them a common ground. This makes for interesting stories about how they interact based on their shared experiences.
One great 'nightwing batgirl young justice fanfiction' is 'The Young Justice Reunion' which focuses on the dynamic between Nightwing and Batgirl within the Young Justice universe. It has a lot of action and great character interactions.
One of the best dynamics is the contrast between Nightwing's practical, physical skills and Zatanna's magical abilities. He can handle the close - combat and on - the - ground situations, while she can deal with threats from a more otherworldly or magical perspective. For example, when facing a horde of demons, Nightwing can fight them off physically while Zatanna uses her spells to banish them back to their realm. Another great dynamic is their friendship or potential romantic relationship. They can have a lot of banter and teasing, which makes their interactions fun to read. For instance, Nightwing might make a joke about Zatanna's elaborate spell - casting gestures, and she would playfully respond with a small magical prank on him.
One interesting fanfiction is 'Nightwing and the Young Justice Rookies'. It tells the story of how Nightwing trains the rookies in the Young Justice team. Also, 'Young Justice: Nightwing's Legacy' is worth reading. It looks at how Nightwing's actions and decisions shape the future of the Young Justice team.
One great story could be 'The Nightwing - Batgirl Alliance'. It focuses on their teamwork and how they handle a new threat in Gotham. They rely on each other's skills, with Nightwing's acrobatic fighting style and Batgirl's intelligence.
One possible plotline could be them teaming up on a mission. Maybe they are sent to a magical realm where Nightwing's combat skills and Zatanna's magic are both needed to defeat a powerful villain. For example, a sorcerer who is using dark magic to corrupt the land and its people. Nightwing could use his acrobatic skills to dodge attacks while Zatanna uses her spells to counter the sorcerer's magic. Another plotline could involve a mystery that they have to solve together. It could be related to a series of disappearances in a city, and they discover that it has something to do with a long - lost magical artifact that Zatanna has some knowledge about. As they work together, they might also start to develop feelings for each other, adding a romantic sub - plot to the story.
Their relationship could start as just comrades in the fight against crime. They respect each other's skills and slowly start to rely on one another more. As they go on more missions together, they begin to understand each other's quirks and personalities better, which deepens their bond.
One idea could be that Nightwing has to train the Young Justice team in some new combat techniques. Maybe there's a new threat in Gotham that requires their combined skills to take on. Another could be a time - travel plot where the Young Justice team gets sent back in time and meets a younger Nightwing, and they have to work together to get back to their own time. Or perhaps Nightwing goes undercover in Young Justice to investigate a mole, leading to a lot of mystery and drama within the team.