A great plot could involve Batman and Robin having a disagreement about how to handle a young meta - human in Young Justice. This could lead to Robin going off on his own for a bit to try and solve the problem his way, while Batman realizes he might need to trust Robin more.
One idea could be Robin trying to prove himself to Batman in a mission within the Young Justice framework. Maybe there's a new villain in town that only they can stop together.
One idea could be that Robin is on a solo mission in Gotham and crosses paths with Catwoman. She initially tries to mislead him, but he sees through her tricks. They end up teaming up briefly to take down a mutual enemy who is stealing valuable artifacts from both the Batcave and Catwoman's hideouts.
Maybe in the fanfiction, the harem members are all from different backgrounds within the Young Justice universe. They are brought together by their feelings for Robin. Some are heroes, some are civilians with special knowledge. Their relationships develop as they help Robin solve a mystery that threatens the entire Young Justice world. This would involve a lot of character exploration and relationship building.
Another plot could involve Robin being forced to work undercover as an assassin in a criminal organization. He has to balance his loyalty to the Young Justice and his mission to take down the organization from the inside. He might face moral dilemmas as he has to pretend to be a cold - blooded killer.
One idea could be that Robin is on a solo mission and Deathstroke is hired to stop him. Robin has to use his wits and agility to outmaneuver Deathstroke's superior strength and experience. Another could be that Deathstroke, for some reason, decides to train Robin secretly, leading to a complex relationship between the two where Robin is conflicted about learning from an enemy.
A great plot could involve Robin getting injured and Cirel having to take care of him. During this time, they have deep conversations and start to understand each other on a more personal level. This could lead to a stronger bond between them in the fanfiction.
One interesting plotline could be Robin trying to prove himself to Batman in a more complex and dangerous mission within the fanfiction world. Maybe there's a new villain in Gotham that only Robin can stop, but Batman is hesitant to let him take the lead at first.
Perhaps in the Young Justice universe, Catwoman discovers a secret about Batman's past that puts her in a moral dilemma. She could either use this information to her advantage or help him keep it hidden. As they interact more because of this, feelings start to develop between them that they didn't expect. They have to navigate their relationship while also dealing with the threats that Young Justice faces.
One idea could be a time - travel plot where Fem Robin and Wally end up in a different era in the Young Justice universe. They have to work together to find a way back while also dealing with the challenges of that time period.
One idea could be that Robin and Wonder Woman team up for a special mission in a hidden, ancient temple. They have to solve puzzles that require both Robin's detective skills and Wonder Woman's knowledge of ancient lore. Another could be a story where Robin gets injured during a battle and Wonder Woman takes it upon herself to train him in new combat techniques to make him stronger.
Maybe there's a plot where they have a misunderstanding at first. Robin thinks Wonder Girl is too reckless in battle, while Wonder Girl believes Robin is too controlling. But through a series of events, they come to understand and respect each other more, and in the end, they become a stronger team.