One main theme is friendship. Harry forms new friendships with the unsullied as he helps them. Another theme is redemption. By helping the unsullied, Harry might be seen as redeeming some of the wrongs in the wizarding world. And of course, there's the theme of heroism as Harry steps up to help those in need.
One popular 'Harry Potter helps the unsullied' fanfiction is 'The Aid of Harry Potter'. In it, Harry uses his magic and knowledge to assist the unsullied in various challenges they face in the wizarding world. Another is 'Harry's Unlikely Alliance' which shows how Harry forms a bond with the unsullied and together they overcome dark forces.
I'm not sure who the author of this fanfiction is. There are so many fanfiction writers out there, and it can be difficult to track down the creator of a specific piece, especially if it's not a widely known one.
The 'harry potter frees the unsullied fanfiction' might be a very unique piece. Given that Harry Potter is often associated with fighting against dark forces and injustice in the original series, in this fanfiction, he could be applying those same principles to the Unsullied. It could explore themes of freedom, heroism, and the power of magic. For example, he might have to outwit powerful enemies who are holding the Unsullied captive, and his friends like Ron and Hermione could also be involved in the mission to free them.
Maybe some of the Hogwarts professors like Professor Sprout. After all, she's the Herbology teacher. She could give Harry some expert advice on how to grow different kinds of food plants. She might even let him use some special greenhouses or tools in the school for his food - growing projects.
Yes, there are some fanfictions out there where the two universes cross paths and Harry Potter might help Superman in some way. You can try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own.
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 great fanfiction where Snape helps Harry Potter is 'The Unseen Bond'. In this story, Snape secretly protects Harry from a new dark threat at Hogwarts. He uses his knowledge of the Dark Arts to counter the enemy's spells. This shows a different side of Snape, one that is more benevolent towards Harry.
One possible plot could be that Superman is somehow transported to the wizarding world. He's lost his powers there, and Harry Potter has to help him get back to his own world while also protecting him from the various magical threats in the wizarding world. Along the way, Harry could teach Superman some basic magic to help him defend himself, and Superman could use his strength and heroism in a different way within the magical setting.
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.