One key moment could be when they protect each other from other villains or Pokémon. Another might be when they share a rare moment of vulnerability after a particularly tough defeat. Also, the times when they come up with plans together, showing their teamwork and the trust they have in each other, are important in their love story.
Meowth would be a great addition. He could provide comic relief while also being part of Team Rocket's adventures related to the lemon theme. Also, Pikachu could be involved. Maybe Jessie and James try to use lemons to attract Pikachu in a new and strange way. And Butterfree, as it could be related to the pollination of lemon trees in the fanfiction.
Ash and his Pikachu would be great to pair them with. There's always been that rivalry between Team Rocket and Ash, and it could lead to some really fun and exciting interactions. Maybe in this fanfiction, they end up having to team up against a greater threat.
Another great character to pair them with could be Professor Oak. Imagine the chaos and hilarity when Jessie and James, the bumbling villains, interact with the wise and knowledgeable Professor Oak. He could be a mentor figure, guiding them towards a new path, or they could be constantly trying to outwit him for some reason.
Well, Jessie and James' love story is a rather interesting one. They are part of Team Rocket, constantly scheming. But beneath all that, there's a connection. They've been through so much together, from getting blasted off by Pikachu countless times to coming up with new plans to capture Pokémon. Their love might not be the typical romantic love at first sight. It's more like a love that has grown out of mutual understanding, loyalty, and the shared experiences of being in Team Rocket.
They might love fanfiction because it offers new perspectives on their own lives. In fanfictions, their characters can be developed in ways that the original show might not have explored fully. For instance, they could be portrayed as more complex individuals with deeper backstories.
As I don't know the real story, a possible key moment could be their first date. It's often a special time when they really start to get to know each other on a deeper level.
I'm not sure specifically as there could be many different versions of such a fanfiction. But generally, it might be about Ash coming to the rescue of Jessie and James in some sort of dangerous or difficult situation they are in within the Pokémon universe.