In such a fanfiction, Harry could have been manipulated by Voldemort through a powerful dark magic spell. Voldemort, seeing Harry's potential, decided to make him his right - hand man instead of killing him. Harry would then be forced to do Voldemort's bidding. He would be involved in dark rituals and battles against the good wizards. However, deep down, he might still have a glimmer of his old self and eventually break free from Voldemort's control.
One possibility could be that Harry was somehow turned to the dark side early on. Maybe he felt betrayed by Dumbledore or the wizarding world. As Voldemort's right - hand man, he would use his knowledge of Hogwarts and the Order of the Phoenix to undermine their efforts. He might lead attacks on the school and help Voldemort in his search for the remaining Horcruxes.
The wizarding world would be in chaos. Harry, being Voldemort's right - hand man, would be a huge threat. He knows many of the Order of the Phoenix's secrets. Hogwarts would no longer be a safe haven. The students would be in constant fear as Harry could use his inside knowledge to help Voldemort attack the school. The Ministry of Magic would also be in a difficult position as they had once relied on Harry to be their savior.
One possible plot could be that Harry is magically transformed into a panther by Voldemort as a form of punishment or control. Harry, in his panther form, has to find a way to break the spell while also trying to gather information about Voldemort's plans. He might use his new form's abilities, like stealth and speed, to his advantage.
Well, it could be that Voldemort has a strange fascination with wolves and decides to turn Harry into one as part of his plan to create a super - being under his command. Harry, in his wolf form, retains his own consciousness and memories. He has to endure the instincts of the wolf while also plotting against Voldemort. He might use the wolf's enhanced senses to gather information about Voldemort's lair and his plans, all while pretending to be under Voldemort's control.
One possible plot could be that the contract is a magical binding that forces Harry to work with Voldemort in some way. Maybe it's a deal to save the lives of his friends. So, Harry has to reluctantly follow Voldemort's orders while secretly looking for a way to break the contract.
One possible plot could be that Harry, being Voldemort's little brother, has been hidden away from the wizarding world by some powerful magic. As he grows up, he starts to discover his true identity and his connection to Voldemort. This discovery throws the wizarding world into chaos as they don't know whether to trust Harry or see him as a threat.
One possible plot could be that Harry discovers a prophecy that in order to truly end the dark magic in the wizarding world, he has to get close to Voldemort by becoming his assassin. So he pretends to be on Voldemort's side, all the while planning his demise.
One possible plot could be that Harry discovers a prophecy that ties his and Voldemort's fates together in a more intimate way than just being enemies. This leads him to seek out Voldemort to understand it better. As they interact, they find themselves attracted to each other. Voldemort, who has always been alone in his pursuit of power, starts to question his motives, and Harry tries to convince him to turn away from the dark path. The plot would be filled with internal and external conflicts as they navigate their relationship and the consequences it has on the wizarding world.
Perhaps the plot could start with Voldemort finding a way to capture Harry and turn him into a cat for his own amusement. Harry, as a cat, has to navigate the dark and dangerous world of Voldemort's lair. He could make unexpected alliances with some of Voldemort's minions who might have a change of heart. Meanwhile, his friends are desperately searching for him, not realizing he's been turned into a cat. As the story progresses, Harry could find a way to reverse the spell and use his new - found knowledge of Voldemort's secrets to finally defeat him.
The plot might involve a new character who is bestowed with the 'Right Hand of God' power. This character could initially struggle with this power as it's so overwhelming. They might be hunted by those who want to take the power for themselves. Along the way, they team up with Naruto and his friends to protect the power and use it for good in the shinobi world.
One possible plot could be that they are forced to join Voldemort under some sort of dark magic compulsion. Maybe Voldemort has a new powerful spell that he uses on them to make them his servants. Then they have to struggle with their own moral compasses while doing his bidding, and secretly try to find a way to break free and defeat him from the inside.