One common theme is the power dynamic. Jhin, being a complex and often powerful character, has different power interactions with the members of his harem. Another theme could be the exploration of relationships, like how Jhin forms different kinds of bonds with each character in the harem.
Another place could be FanFiction.net. However, the quality may vary a lot. You need to browse through different stories, read the summaries and reviews to find the ones that suit your taste for Jhin x Harem fanfiction.
Another theme is the idea of the hunter and the hunted. Caitlyn is a hunter by nature, always seeking to bring criminals to justice. Jhin, on the other hand, is like a wild card, a hunted yet elusive figure. Their relationship in the fanfiction often plays on this dynamic, with Caitlyn chasing Jhin or vice versa. It makes for some really exciting chase scenes and psychological battles.
The theme of mystery also pops up often. Given Jhin's secretive and elusive nature, fanfictions might revolve around Sona trying to uncover the real Jhin. And on the other hand, Jhin might be intrigued by Sona's silent yet powerful presence. Their relationship developing as they both peel back the layers of each other's mysteries can be a very engaging theme in Sona x Jhin fanfiction.
I also like 'Silent Stalkers'. This fanfiction imagines a world where Jhin has a new target in Piltover, and Caitlyn is determined to stop him before he strikes. The author does a great job of building up the suspense between the two characters as they engage in a cat - and - mouse game throughout the story.
Jhin's back story involves a traumatic past that shaped his twisted view of art and violence. He was once a normal person but underwent a series of events that drove him to become the deranged killer we know.
You can try searching on fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. They usually have a large collection of fanfictions on various topics, including those related to Sona and Jhin.
Sakura could be one of the members. She has always had a complex relationship with Naruto. In this harem scenario, her feelings could evolve further. Hinata is also a likely candidate. Her long - standing admiration for Naruto might lead her to be part of the harem. Tenten could also join, perhaps drawn in by Naruto's growth as a ninja.
Well, obviously Rias herself would be a central member. Then there could be Akeno Himejima. She has a mysterious and alluring personality, and her relationship with Rias could be an interesting dynamic when Naruto enters the picture. Also, Koneko Toujou, with her cute and somewhat tsundere nature, might be another member. She could be initially cold to Naruto but gradually warm up to him.
Well, Mirajane could be part of the harem. She has a motherly side and would want to comfort Natsu if he was betrayed. Levy is also smart and resourceful, and she could use her skills to help Natsu out. Juvia, with her obsessive love for Gray, might transfer some of that intense loyalty to Natsu if she saw him in a desperate situation after being betrayed.