Maybe the OC is a healer who has a secret past. Naruto meets her when he is injured during a mission. As she heals him, he becomes curious about her. The other characters in the harem also get involved as they too need her healing services at some point. She has a mysterious charm that attracts them all. She might be hiding a connection to an ancient ninja clan, and as the story unfolds, the harem members help her uncover her past while falling deeper in love with her.
One idea could be that the OC is a powerful ninja from a far - off land. She comes to Konoha and catches the attention of Naruto and his friends. As she gets to know them better, she forms unique bonds with each of them, leading to a harem - like situation. For example, she might train with Naruto and they share their dreams of becoming Hokage and protecting the village. With Sasuke, she could be someone who understands his pain and tries to bring him back to the light. And with others like Shikamaru, she might engage in strategic battles and discussions, slowly building relationships.
The OC could be a descendant of a powerful clan that was thought to be extinct. Their presence in the Naruto world stirs up interest among many characters. The OC's knowledge of ancient jutsu and their kind heart draw in characters like Kakashi, Shikamaru, etc. into a harem. The OC then has to navigate the complex relationships while also trying to keep their clan's secrets safe.
One idea could be that the OC has a special power that attracts Natsu and the other harem members. For example, the OC can control a unique type of magic that is crucial in saving the world, and Natsu is drawn to her courage. Another plot could involve the OC being from a different dimension and Natsu has to help her adapt to his world while falling in love. And perhaps there could be a rival in the harem who tries to drive the OC away from Natsu.
One idea could be Naruto somehow finds himself in a situation where he has to team up with Tayuya frequently. As they interact more, a harem starts to form around Naruto, with Tayuya being one of the key members. The plot could involve them going on missions together and Naruto gradually realizing his feelings for Tayuya among the others in the harem.
One idea could be the OC having a unique power that attracts the various characters in the harem. For example, if the OC can manipulate time in a certain way, it could lead to some really interesting situations. Maybe they use this power to save a member of the harem from a dangerous situation, which then makes that character develop strong feelings for the OC. Another plot idea is the OC being from a different dimension and having to adapt to the Highschool DxD world while building relationships with the harem members.
One idea could be an OC with a unique power that attracts the attention of multiple X - Men characters, leading to a harem - like situation. For example, an OC who can manipulate time on a small scale. This power could be both useful and dangerous, and different X - Men might have different reactions to it, some being intrigued and others being cautious.
One idea could be that the OC is a new fighter in the Mortal Kombat tournament. As they progress, they attract the attention of various characters from different realms who then form a harem around the OC. Maybe the OC has a unique power that intrigues them all.
One idea could be that Naruto accidentally enters a different dimension where he meets Fuu and gradually attracts other characters who form a harem around him. They could go on adventures together, fighting against new threats in that dimension while Naruto tries to find his way back home.
Maybe an evil villain casts a spell on Naruto that draws a harem of female ninjas to him, thinking it will distract him. But Naruto uses this new situation to his advantage. He has the girls help him train in new ways and they all form a unique bond as they work together to face the real threats to the village.
One idea could be that Naruto, while on a mission in an unknown land, meets Guren and gradually other characters are attracted to him, forming an unexpected harem. Maybe Naruto's unique ninja skills and his kind heart draw them in.
A more complex plot could be that there is a powerful enemy that threatens both Naruto's world and the world of Rias. Naruto and Rias's harem have to team up to defeat this enemy. Along the way, they face many challenges that test their abilities and relationships. Naruto's positive attitude and never - give - up spirit start to influence the members of the harem, and they in turn show Naruto new ways of using magic and power.