Well, of course, Ruby would be a common character. She's the main protagonist in RWBY, so it's natural for her to be part of the story. Yang Xiao Long could also be involved. Her protective and fiery personality would add a lot to the harem dynamic. Pyrrha Nikos might also be included. Even though she had a tragic end in the original series, in fanfiction, she could have a new role in the OC's harem, adding an element of redemption or second chances.
One interesting concept could be the reincarnation aspect. It allows for the OC (Original Character) to have a new start in the RWBY universe, perhaps with knowledge from their past life that gives them an edge. Another concept might be the harem part, which could lead to various relationship dynamics and character interactions within the story.
First, give each character in the harem a distinct personality. For example, one could be a strong and silent type, while another is very outgoing and bubbly. Then, show how they interact with the OC. Their reactions to the OC's reincarnation and unique traits can shape their development. For instance, if the OC has a special power, some characters might be in awe, while others could be jealous.
Obviously Ruby herself is a main character. She is the center of the reincarnation concept. Weiss, Blake, and Yang are also important as they are Ruby's team members. Their relationships with Ruby are likely to be explored in different ways in the fanfiction due to Ruby's reincarnation. Ozpin could also be involved as he has a lot of knowledge about the history and secrets of Remnant, and Ruby's reincarnation might be related to some of those deeper mysteries.
Naruto himself is often involved. Since it's a Naruto fanfiction, the main character of the original series is likely to play a big role. He might interact with the oc, perhaps helping them adjust to the ninja world. Sasuke is also a popular character in these fanfictions. His cool and brooding nature can create interesting dynamics with the oc.
One idea could be that the OC reincarnates into the RWBY world with some unique powers from their past life. These powers attract the attention of different characters, gradually forming a harem. For example, their power could be related to some ancient magic that is both feared and desired in the RWBY world.
A prevalent theme is the discovery of self - identity. The OC, while in the middle of a harem situation, also has to figure out who they are in this new world of Remnant. They might have to deal with their past, their new - found powers, and how they fit into the RWBY universe. And of course, the theme of love and romance is central, with different ways of showing affection and dealing with the complexity of having multiple romantic interests.
Harry Potter himself is often a common character. He might be the one who accidentally stumbles upon the hypnosis magic and ends up with a harem. Hermione Granger is also frequently included. Her intelligence could be used in different ways in the story, like helping to understand the hypnosis magic better or being an important part of the harem dynamic. Ginny Weasley is another character that can be part of the harem. She has her own strong - willed personality that can add interesting twists to the story.
Luna Loud is also a popular character in such fanfictions. Her cool and unique personality might attract multiple characters towards her, leading to a harem - like plot. Her love for music could be a factor that draws other music - loving characters to her in the fanfiction.
Oliver Wood is another character that might be in such fanfiction. He's extremely passionate about Quidditch. In a harem - related Quidditch fanfiction, he could be the object of affection for some students who are attracted to his dedication and skill on the pitch. Also, the Weasley twins, Fred and George, could be involved. Their mischievous nature combined with their Quidditch skills might draw a group of followers or love interests.
Definitely Naruto has to be at the center. But aside from the obvious ones like Sakura and Hinata, characters like Anko Mitarashi can also be part of the story. She has a unique personality that can add a lot of spice to the harem jutsu - related plot. Also, Kurenai Yuhi could be involved. Her calm and composed nature contrasts with the chaos that the Harem Jutsu can bring. And don't forget about Karin, who has her own history with Naruto and could be an interesting addition to the harem in fanfiction.