Most 'Harry Potter' fanfiction follows the path of good versus evil as in the original books. Harry is typically portrayed as opposing Voldemort, not helping him resurrect. However, if you search on some large fanfiction platforms like Archive of Our Own, you might find something, but it won't be a common or popular theme within the fan community.
One possible plotline could be that Harry is under some sort of dark magic influence or curse that forces him to aid in Voldemort's resurrection. Maybe a powerful dark wizard has manipulated Harry's mind.
One popular 'harry helps voldemort fanfiction' could be 'The Unlikely Alliance'. In this fic, Harry realizes that there are greater threats and teams up with Voldemort to face them. It has an interesting take on their relationship and how they navigate their differences to work together.
One common theme is redemption. The idea that Voldemort can be saved or changed through Harry's help. Another theme is the exploration of power dynamics. Since Harry and Voldemort have very different views on power, seeing how they interact when Harry is trying to help can be really interesting.
Yes, there are some out there. Some fanfictions might explore the idea of Harry Potter helping Voldemort in an alternate universe where their goals are misaligned or there are complex magical reasons for it. For example, in a situation where Harry believes he can change Voldemort's ways by getting closer to him, rather than fighting him directly.
One possible plot is that Harry discovers a hidden prophecy that says only by helping Voldemort can he truly save the wizarding world in the long run. So, he reluctantly starts to assist Voldemort in his conquests, all while secretly planning to turn the tables.
Often in fanfiction, Dumbledore helps Harry understand the nature of Voldemort's soul - splitting into Horcruxes. He may guide Harry in the search for these Horcruxes. Dumbledore could also use his own powerful magic to shield Harry from Voldemort's attacks, at least until Harry is fully prepared for the final confrontation.
One great 'Harry and Voldemort soulmates fanfiction' is 'The Soulmate Bond'. It delves into how their fated connection affects the wizarding world. The author creates a really interesting dynamic between them, exploring how their opposite natures are still intertwined on a deeper level.
I'm aware of the existence of such fanfictions. In these stories, the implications are huge. If Harry were Voldemort's son, the whole dynamic between good and evil in the wizarding world would be completely altered. It would also change the significance of the prophecy. Harry's struggle against Voldemort would take on a whole new meaning, perhaps more of an internal conflict within a family rather than a fight between two separate entities. Many of these fanfictions delve deep into these complex ideas, making for an interesting read for those who enjoy exploring alternate storylines in the 'Harry Potter' world.
Often in fanfiction, their relationship can change drastically. They could end up as allies, which would require both of them to change. Harry would have to see past Voldemort's evil deeds, and Voldemort would have to let go of his hatred for Harry. This exploration of character change makes fanfiction so interesting.
Harry often becomes more conflicted. He has always seen Voldemort as the ultimate evil, but now being mates, he has to re - evaluate his views. He might start to see the humanity in Voldemort, which makes him question his own beliefs and actions in the fight against the Dark Lord. For example, he may hesitate in battles more than before.