Definitely, Tsunade from Naruto would be a prominent female character. She's strong, authoritative and has a lot of wisdom. From One Piece, Rebecca could be part of the harem. She has her own story of growth and determination. And then there's Vivi. She cares deeply about her people and has a kind heart. These female characters would all interact differently with the male characters from Naruto and One Piece, creating a complex and interesting harem fanfiction.
Naruto would probably be really curious about the Devil Fruits in the One Piece world. The female characters like Nami might be initially cautious of him but then intrigued by his ninjutsu. For example, when Naruto uses his Rasengan, they would be amazed. And Naruto would be in awe of the Grand Line and all the strange islands, while the girls would show him around.
The main characters could also be Sasuke from Naruto and Gray from Fairy Tail. Sasuke's cool and brooding nature combined with his Sharingan abilities would be a draw. Gray's ice - make magic and his habit of accidentally stripping could add some humor. In the harem, characters like Ino from Naruto and Levy from Fairy Tail could be part of it. Ino's mind - control jutsu and Levy's intelligence with books and runes would bring different elements to the story.
Another option could be a new character entirely. This character could be a hybrid of the two worlds, having some abilities from Naruto and some from One Piece. His unique background and skills would make him stand out, and as he tries to find his place in this combined world, he could attract a harem of female characters. He could be on a quest to bring peace between the two worlds, and during this journey, he builds relationships with various female characters.
Nami would be a great addition. She's strong - willed, intelligent, and has a complex personality. Her relationship with the male crew members already has some interesting dynamics, and in a harem scenario, her interactions with them could be explored further, especially with her love for money and how that might play into her relationships.
Naruto with the Rinnegan would be an even more powerful force. He could use his new - found powers to quickly adapt to the One Piece world. For example, he might use the Rinnegan's ability to see chakra to detect devil fruits or sense hidden treasures. Luffy would be his usual carefree self but would be very curious about Naruto's abilities. He would probably want to have a friendly fight with Naruto to see who is stronger.
Sakura could be one of the main female characters. She's strong - willed and intelligent. Her medical knowledge and combat skills would make for interesting interactions with Ichigo. Hinata is another possibility. Her shy nature and her Byakugan abilities could lead to some unique moments with Ichigo. And then there's Ino. With her mind - control jutsu, she could have some really fun and complex relationships with Ichigo in the crossover.
From Naruto, Tenten could be in the harem. She is a skilled weapon user. In the DBZ universe, Marron could be part of it. She is Krillin's daughter and could have her own story arc in this harem situation. Also, Pan from DBZ, being Goku's granddaughter, could be an interesting character in the harem with her Saiyan blood and adventurous spirit.
From the Naruto universe, Sakura would be a likely candidate. She's strong - willed and has a history of being attracted to powerful guys like Sasuke, so Naruto's new - found crossovery powers could draw her in. In the Percy Jackson world, Annabeth is smart and independent. She might be intrigued by Naruto's different fighting style and unique upbringing as a ninja. Also, Piper has the ability to charm - speak, but she could also be charmed by Naruto's genuine nature.
It's really hard to say. Luffy has his Gear Fourth form and the ability to stretch his body in incredible ways. But Naruto in his Sage of Six Paths mode is extremely powerful too. He has access to a vast amount of chakra and can use some of the most powerful jutsu. However, if we consider Kaido from One Piece, with his near - indestructible body, he would also be a top contender. So it could be any of them depending on how the crossover is written.
It's hard to say for sure. Luffy has the power of the Gum - Gum Fruit and his Haki, which gives him great strength and the ability to sense and overpower opponents. However, Naruto has the Nine - Tails' chakra and Sage Mode. In a crossover, if they were to fight, it might depend on the situation. But if we consider all - round power, Naruto's ability to create multiple clones and use a variety of jutsu might give him an edge over Luffy in some scenarios.