Yes, there are quite a few. You can check some fanfiction websites like FanFiction.net. Just search for 'pokemon james harem' and you'll likely find a variety of stories, but the quality may vary.
One common theme is friendship. Since James is a character from the Pokemon world, his relationships with the members of the harem often involve elements of friendship that develop into deeper bonds. Another theme could be adventure, as they might go on Pokemon - related adventures together.
One possible fanfiction could be that James loses his beloved Weezing in a battle. He has had Weezing since he was a child, and it was like his only true friend in Team Rocket. So when it faints and doesn't get up, he starts crying. He realizes how cruel the world of Pokemon battles can be and has a moment of self - reflection about his life in Team Rocket.
In Pokemon fanfiction, James is often portrayed as more complex than in the original series. He can be shown as having a softer side, especially when it comes to his Pokemon. For example, he might show more empathy towards their needs and feelings.
In 'pokemon james fanfiction', a frequent theme is growth. James grows as a character, whether it's in his skills as a trainer or in his moral compass. The theme of identity also pops up a lot. He questions who he really is, especially when he's away from Team Rocket. And adventure is a big theme too. He goes on various adventures that test his limits and change him. For instance, he might go on a quest to find a special pokemon or explore a new region, which all contribute to his development as a character. This is what makes these fanfictions so engaging and interesting to read.
Meowth would probably be overjoyed. He has been with Jessie and James for a long time and would see their marriage as a great thing. He might be more helpful than ever, running errands for them and even trying to cook for them using his little paws. Their other Pokemon like Ekans and Koffing might be a bit confused at first but would soon get used to the new situation and be protective of their new 'family'.
A common theme in such fanfictions could be Ash's adventures in Alola while building relationships with different characters. Maybe he forms special bonds with his Pokémon and the people around him in a more romantic or friendship - deepening way.
Ash is of course a very common character as he is the central figure. Pikachu is also often included as it is Ash's most well - known Pokémon. Other characters like Misty and Brock might also make appearances as they are Ash's friends and travel companions in the original Pokémon series.
In the fanfiction, James' sister might be a Pokemon researcher. She is intrigued by the legendaries and sets out to study them. She teams up with some other trainers and together they explore ancient ruins. They face many challenges, like Team Rocket trying to steal their findings. But James' sister is smart and uses her knowledge of Pokemon behavior to outwit them every time.
One great Pokemon Reborn Harem Fanfiction is 'A New Journey in Reborn'. It has an interesting plot where the main character gradually builds a harem of different Pokemon trainers. The character development is well - done, and it shows how they all interact and grow together.