Well, 'Konosuba: God's Blessing on this Wonderful World!' is a must - mention. Kazuma is reincarnated in a fantasy world and teams up with a group of misfits, including some female characters who form a sort of harem around him. It's known for its humor and unique take on the isekai genre with harem elements.
One popular one is 'The Rising of the Shield Hero'. It features a unique isekai setting where the protagonist is summoned to another world as the Shield Hero, and gradually forms a harem of diverse characters throughout his adventures.
One popular harem isekai light novel is 'In Another World with My Smartphone'. The protagonist is transported to a fantasy world with his smartphone and soon finds himself surrounded by various female characters. Another is 'Overlord', where the main character, Momonga, is trapped in a game world and has interactions with different female npcs that could be considered part of a harem - like situation. And 'The Rising of the Shield Hero' also has elements of harem isekai, with the main character, Naofumi, gradually gathering a group of female companions during his adventures in the isekai world.
One popular 'isekai harem novel' is 'No Game No Life'. In this story, the two main characters are transported to a different world filled with games and rules. They encounter various female characters, and a harem - like dynamic develops as these characters are drawn to the protagonists' intelligence and unique abilities.
If you're new to isekai harem light novels, start with 'No Game No Life'. It has an interesting concept and the harem aspect is more about the relationships based on the game - playing. 'High School DxD' is also a popular choice, but it has some more mature themes, so be aware. However, the story is exciting and the harem is a big part of the plot.
Love and relationships are also key themes. The development of relationships between the protagonist and the members of the harem can range from simple friendship to deep romantic love. These relationships often face challenges, like jealousy among the harem members or external threats to the group, which adds drama to the story.
Yes, I recommend "The Legend of Concubine Hui in the Harem." It's also an ancient romance novel. It also involves the power struggle in the harem and the story line of the female protagonist entering the harem. I hope you like this fairy's recommendation. Muah ~😗
I'm not sure about its popularity. It might be popular within the niche of isekai and harem - loving audiences, but it may not be as well - known to a broader readership.
I'm not sure specifically as I haven't read it in detail. But generally, 'isekai' often involves a character being transported to another world. 'Harem' usually implies a story with a male lead and multiple female characters in some sort of relationship. So it might be a novel about a character in an isekai setting with a harem - like relationships.