One potential ally could be Neji. Neji has his Byakugan and his skills in combat. He could see the dark swordsman as an equal in terms of combat ability and form an alliance. Also, Tenten, who is fascinated with weapons. The dark swordsman's sword and his skills with it could draw Tenten's interest, and she might become an ally. They could exchange knowledge about different weapons and fighting techniques.
There could be some disillusioned wizards who have lost faith in the current state of the wizarding world. They might see the Dark Prince as a way to change things, even if his methods are dark. These wizards could be those who have been marginalized or have suffered losses during the war. They believe that the Dark Prince has a vision for a different kind of wizarding society, not realizing the full extent of his dark intentions.
In this fanfiction, the Dark Prince might find allies among those who have been wronged by the Ministry of Magic. If there are wizards who have been unjustly punished or whose families have been persecuted, they could be swayed to join the Dark Prince. There could also be some international dark wizards who see an opportunity to expand their influence in the British wizarding world through an alliance with the Dark Prince. Another possibility is that there are some dark entities from other dimensions or realms that the Dark Prince manages to summon and convince to be his allies.
Spyro's original friends like Cynder could be potential allies. She has a connection with Spyro and might be able to understand his dark side and help him control it.
Kakashi could be a potential swordsman character. He's known for his combat skills. In the harem, Hinata could be there. Her gentle nature would contrast with the action-packed world. Also, Ino could be part of it, using her mind - control jutsu in unique ways to protect the group and be involved in the harem's relationships.
One interesting plotline could be the dark swordsman's origin. Maybe he was once a regular ninja who was betrayed and then turned to the dark side, finding power in the art of the sword. Another could be his interactions with the main Naruto characters. For example, his battles with Sasuke, where they both have different sword - based fighting styles, which could lead to some epic showdowns.
Natsu could be one of her potential allies. Since he is a dragon slayer himself, he could understand some of the challenges Lucy faces as a Dark Dragon Slayer. He might offer his fire - based powers to complement Lucy's dark dragon slaying abilities. Another could be Erza. With her strong combat skills and leadership, she would be a great asset in battles against dark dragons. Erza could also protect Lucy when she is still learning to control her new powers.
Sabrina could also find an unexpected ally in a magical creature. Maybe a talking cat or a friendly spirit that has knowledge about the Dark Lord's weaknesses. This creature could guide Sabrina on her journey to either defeat or at least resist the Dark Lord. It could be that this creature has a long - standing grudge against the Dark Lord and sees Sabrina as a means to finally get revenge.
Sasuke could be one of the main characters to interact with Dark Naruto. Given their complex relationship in the original Naruto series, Sasuke might be either drawn to help Dark Naruto because of their shared past, or he could see Dark Naruto as a threat to his own goals and power. They could have some intense battles or deep conversations about the nature of power and the path they've both chosen.
One potential ally could be Artorias. He is a powerful knight and his sense of justice might lead him to protect Priscilla. Priscilla's gentle nature might also appeal to him. Then there's Quelana of Izalith. She has knowledge of powerful magic and could potentially help Priscilla control or develop her own powers. And don't forget about Oscar. He is an adventurer at heart and might befriend Priscilla and help her explore the world beyond her painting.
Rock Lee could be a main character. His unwavering determination and his unique taijutsu skills could make for some exciting fight scenes against the evil swordsman. And Hinata, with her gentle yet strong nature. She might be the one who discovers some of the swordsman's weaknesses through her observant nature and then shares this information with Naruto and the others.