You can try fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. Just search for 'Babs and Nightwing Teen Titans' on their search bars.
A really interesting plot could be a time - travel story where Babs and Nightwing are sent back in time to when the Teen Titans first formed. They have to adapt to the past while also trying to find a way back, all the while dealing with their feelings for each other in a different time period. This could bring out new aspects of their characters and their relationship. There could be challenges like trying not to change the future too much and also facing the differences in how the Teen Titans operated back then.
One interesting storyline could be Nightwing joining the Teen Titans on a mission to stop a powerful new villain who has the ability to manipulate time. This would create a lot of chaos and force the team to think on their feet. Another could be Nightwing having to train a new and inexperienced member of the Teen Titans, leading to some comical and also heartwarming moments as they bond.
Obviously, Nightwing himself is very popular. His skills, charm, and his connection to Batman make him a central figure. Starfire is also quite popular in these fanfictions. Her alien powers and her unique personality add a lot of flavor to the stories. Beast Boy is another one. His ability to transform into different animals often leads to some really interesting and funny scenarios in the fanfiction.
The Teen Titans would react with a combination of fear and courage. Starfire, being from another planet, might have some knowledge about the invaders which could be useful. But she'd also be worried about her new home, Earth. Cyborg would probably be excited to take on the new technology of the aliens, seeing it as a challenge to improve his own. Raven, on the other hand, would be more cautious and try to sense any dark motives behind the invasion.
The Teen Titans came into existence as a group of young superheroes. Each member had their own origin story. For example, Robin was originally Batman's sidekick. He brought his skills and determination to the Teen Titans. Starfire came from another planet, Tamaran, and she had superhuman strength and the ability to fly. Cyborg was a result of a scientific experiment gone wrong in a way, which gave him his cybernetic enhancements. Beast Boy could transform into different animals due to an experiment. Raven had her own mysterious background related to her demonic father. Together, they formed the Teen Titans to fight crime and protect the world.
He might try to engage Slade in conversation. Nightwing is smart and could be looking for a way to psychologically get an edge over Slade. He could be probing for Slade's motives, hoping to find a way to turn the situation around. He might also be stalling for time, waiting for the right moment to make his move.
The formation of the Teen Titans had several important events. Robin, having grown as Batman's sidekick, felt the need to step out on his own and lead a team of young heroes. This was a crucial starting point. Then, Starfire's journey to Earth was a major event. She crashed on Earth and her powers and alien nature attracted the attention of others who would become Titans. Cyborg, who was dealing with his new cybernetic body, saw an opportunity to be part of something bigger. Beast Boy, who had always been different because of his shape - shifting abilities, found a group that accepted him. Raven, with her complex powers and background, also joined, and together these events led to the formation of the Teen Titans.
It adds variety. There are so many different ways to interpret the Teen Titans characters, and this fanfic offers one more unique take. It gives fans who are interested in this particular concept (futa Beast Girl) something new to enjoy.