One common theme is the growth of the male protagonist. In these light novels, the male lead often starts as an ordinary or somewhat perverted guy and through his interactions with the girls in the harem, he gradually matures. For example, in 'High School DxD', Issei becomes stronger and more responsible as he faces various challenges with his harem members.
Typically, they often have a school - based setting. This allows for a lot of interactions between characters in a relatively closed environment. For example, in 'High School DxD', the school setting is a major part of the story. Another characteristic is the presence of a male protagonist who is usually surrounded by female characters. This creates opportunities for those ecchi moments. In 'To Love - Ru', the male lead is constantly in situations with multiple female characters.
One great ecchi anime with a good story is 'High School DxD'. It follows the story of Issei Hyodo, a perverted high school student who gets killed and is then reincarnated as a devil. Alongside the ecchi elements such as the fan service of the female characters in revealing outfits, there is a complex story involving battles between different supernatural factions, Issei's growth as a devil, and his relationships with his friends and love interests.
Another great ecchi light novel is 'To Love - Ru'. It's about an alien girl named Lala who comes to Earth and gets involved with a high school boy named Rito. There are numerous comical and ecchi situations as Rito tries to deal with Lala's advances and the chaos that follows her presence.
A good example is 'Sakura Spirit'. It has an interesting plot along with some ecchi content. The art style is quite appealing. There's also 'HuniePop', which combines dating - sim elements with a bit of ecchi. You get to interact with different characters and the game has a unique gameplay mechanic that ties in with the story and the ecchi aspects.
'Attack on Titan' has some really remarkable characters. Eren Yeager is a complex protagonist, his transformation from a revenge - driven boy to a more nuanced character is fascinating. Mikasa Ackerman is a strong and loyal friend, and Levi Ackerman with his cool and deadly combat skills is a fan favorite. The story of humanity's fight against the Titans, the mystery behind their existence, and the political intrigue within the walls make it a gripping anime.
One popular 'ecchi harem light novel' is 'High School DxD'. It has an interesting story with a harem of female characters and some ecchi elements in it. The protagonist, Issei Hyoudou, is a perverted high school student who gets involved in the supernatural world and forms relationships with various girls.
Well, 'Haganai: I Don't Have Many Friends' is an ecchi novel worth mentioning. It's about a group of misfits trying to make friends and there are some ecchi - like situations that add a certain charm to the story. 'Kiss x Sis' is also an ecchi - heavy novel, which tells the story of a boy living with his two step - sisters and the various comical and ecchi situations that arise. Additionally, 'Sekirei' is an interesting ecchi novel that combines battles and relationships with a good dose of ecchi content.
'Haganai: I Don't Have Many Friends' is also suitable. It's about a group of loners in high school who form a club. There are some ecchi undertones, especially with the interactions between the male and female characters. It's more about the characters' growth and their attempts at making friends while having some comical and slightly ecchi moments.
I would also recommend 'Katawa Shoujo'. While it does have some ecchi aspects, it is also very much about the characters' growth and relationships. It's a good entry - point as it shows that ecchi visual novels can be more than just about the risqué content. The writing is engaging and the different story paths make it interesting for new players to explore.