Ashs-many-girls

Once I get chapter two of Pokémon Restart up, the focus will be on them, with an anime version of the female playable character from the gen one games and Adventures Manga being there too for about seven to ten chapters before going from being part of the group to a recurring character. If you look under the Pokémon section of fanfiction.net, you can set character specific tags so that you can look them using the three of them as tags. I'm not sure what you'd consider good as far as quality goes, because different people have different tastes. One fanfiction series I recommend is the Pokémon Reset Bloodlines series. Serena hasn't got a main role in it yet, outside of side stories, but her being added to the harem has been confirmed to eventually happen. Reset Bloodlines has inspired me to let others make side stories for Pokémon Restart, but not many people have taken me up on that.

Here's some Pokémon Related things that have been done for or by me, many of them involve an Ash pairing with at least one of the girls you've listed:

www.deviantart.com/starfighter…

One the other fanfiction on it has me wake up in Serena's body, and as I'm a guy who has ended up in the body of a straight girl, I'm completely at the mercy of her hormones in it.