In a fanfic scenario, perhaps Ivy and Harley are friends and they come across Bruce. They initially have a conflict with him, but then Lemon enters the story. Lemon could be a mediator of sorts. Maybe Lemon has the ability to calm Ivy's plants or Harley's chaotic nature, and helps them to see Bruce in a new light and work together towards a common goal like saving Gotham from a new threat.
I highly recommend 'Partners in Crime'. In this fanfic, Harley and Ivy team up to take on some new villains in Gotham. It's full of action and at the same time, shows their relationship evolving. Another one is 'Under the Stars'. It has a more romantic tone as they go on a camping trip together, away from the city lights, and discover new aspects of their relationship while enjoying the beauty of nature.
Character development is key. Harley's journey from being Joker's sidekick to finding her own identity with Ivy by her side. And Ivy's growth as a character, her connection to nature and how that affects her relationship with Harley. Also, a unique plot. Maybe something like they go on a quest to save a part of Gotham's nature that's being destroyed, which ties in with Ivy's character. It should also have good dialogue that reflects their personalities, like Harley's crazy but endearing one - liners and Ivy's more serious, nature - centric statements.
One great 'Harley Quinn x Poison Ivy Fanfic' is 'Green and Red'. It really delves into their complex relationship, showing how they support each other through different challenges in Gotham. The way it describes their interactions is both true to their characters and also adds a new layer of depth to their bond.
One possible scenario in this fanfiction could be Naruto finding himself in the chaotic world of Harley Quinn and Poison Ivy. Maybe Naruto's ninja skills would be put to the test against the various villains in their world. He could use his shadow clone jutsu to confuse enemies like the Joker or other foes that Harley and Ivy often face.
The plot could involve a heist. Harley and Ivy plan a heist, and Bruce is on the case to stop them. Lemon could be an unexpected accomplice of Harley and Ivy. For instance, Lemon might have some inside knowledge of the place they are targeting. As the story unfolds, Bruce might start to understand the motives of Harley and Ivy and try to find a way to resolve the situation without just arresting them.