Well, in some fanfics, it could be Anko. She has a wild side and her own set of skills. Her bold personality might intrigue Kakashi. Also, Tsunade could be a love interest in a more complex and mature - themed fanfic. Given her leadership and power, it could make for an interesting dynamic with Kakashi. And then there's always the possibility of a foreign ninja who comes to Konoha and catches Kakashi's heart.
A potential love interest could be a young and upcoming ninja in the village. Maybe she's a new genin who shows great potential. Kakashi, being a mentor - like figure, could start to have deeper feelings for her as he watches her grow. Or it could be a kunoichi from a different hidden village who comes to Konoha on a diplomatic mission and she and Kakashi end up falling for each other.
Perhaps a fellow hacker who understands his world. They could bond over their shared skills and knowledge of the digital realm. Another option could be a civilian who is initially unaware of his double life but gradually gets drawn into it and falls in love with him despite the risks.
Nagisa could be one. He has a kind heart and is very intelligent, which could attract the main character. Also, Karma's confident and somewhat rebellious nature might make him an interesting addition to the harem in a unique way. And Kayano, with her cheerful personality and hidden secrets, could also be a potential love interest.
Perhaps a mortal with a special gift for metallurgy or some other craft related to Hephaestus' work. This mortal could be seen as an equal in terms of skill, at least in a way that catches Hephaestus' eye. They would bond over their shared love for the craft, and over time, this bond could turn into a deep, loving relationship. Hephaestus might be drawn to the mortal's unique perspective and the way they approach the craft despite not having the same divine powers as he does.
Hinata is a very obvious choice. She has always had deep feelings for Naruto. In a fanfiction, their relationship could spiral further, exploring more of their shared interests, like their love for the village and their dreams for the future of the ninja world.
One potential love interest could be Rock Lee. His unwavering dedication to his training and his positive attitude could be appealing to Naruto as a female. They could bond over their shared values of hard work and perseverance. Another could be Itachi, if the story takes a different turn and he's still alive. His mysterious and complex nature might draw Naruto in, and they could have a relationship that's full of intrigue and understanding, especially considering Naruto's new identity as a female.
There could be an older, more mature character, like a college student who she meets by chance and who is drawn to her unique charm and innocence.
Ezra might also be a possibility. He could be involved in a complex relationship with Spencer where he has to deal with her pregnancy and all the emotions that come with it.
If it's a crossover with the Percy Jackson universe, Percy himself could be interested in Ruby. They both have a sense of adventure and a desire to protect their friends. Annabeth might find herself drawn to Weiss because of their shared intelligence and strategic thinking. Leo Valdez could have a crush on Yang due to her mechanical skills and fiery personality. And Nico di Angelo might be intrigued by Blake because of her mysterious nature. These could all be great potential love interests in a RWBY - Percy Jackson crossover harem fanfiction.
It could be a figure skater. Maybe a rising star in the skating world who Bella meets at a competition and they strike up a connection. He might be drawn to her passion for the sport.
Perhaps a fellow duelist who has always been in her shadow. He respects her skills and is always there to support her. Over time, this admiration turns into love. He might be the one who helps her in tough situations and through their shared love for the game, they grow closer.