A possible plot could be that in a post - Voldemort era, Harry Potter, as the Master of Death, is exploring different magical dimensions. He stumbles upon the realm of Aphrodite. Aphrodite mistakes him for a lost soul and tries to guide him with her love. But Harry realizes that there are dark forces at work in her realm too. He uses his knowledge of death and resurrection to help Aphrodite fight off these dark forces that are threatening to corrupt her domain of love and beauty.
Another plot might involve Aphrodite falling in love with Harry Potter because of his unique status as the Master of Death. She decides to use her powers to make him the most desirable being in the wizarding world. However, this causes chaos as witches and wizards from all over start vying for his attention. Harry has to use his skills and the power of the Deathly Hallows to restore order and convince Aphrodite that her actions are causing more harm than good.
One interesting plot could be that Harry Potter, as the Master of Death, encounters Aphrodite in the wizarding world. Maybe Aphrodite is intrigued by the concept of death in the wizarding realm and wants to learn more. Harry, in turn, is fascinated by her powers of love and beauty. They could team up to help a young wizard who has lost all hope and love due to a dark magic curse, with Aphrodite using her love - inducing powers and Harry using his mastery over death to free the wizard from the curse's hold on his soul.
Harry Potter's power as the Master of Death gives him a certain control over life and death. Aphrodite's power is centered around love and beauty. Their powers could interact in a way that when Harry faces a situation where a character is on the brink of death due to a lack of will to live (perhaps because of a broken heart), Aphrodite could use her love - based powers to revive their will, and then Harry could use his power over death to heal any physical ailments. For example, if a wizard has been cursed and is dying while also losing the will to fight, Aphrodite could make them feel love again, and Harry could reverse the curse's deathly effects.
One interesting plot could be her using her Aphrodite - given charm to navigate the wizarding world. For example, she might use her allure to befriend some of the more difficult characters in Hogwarts, like Snape. Another plot could involve her love life being affected by her Aphrodite heritage. Since Aphrodite is the goddess of love, she could find herself in complex romantic situations that are different from the normal wizarding romances. Maybe she has the power to make people fall in love with her accidentally, and she has to learn to control it to avoid chaos at Hogwarts.
A common plot in such fanfictions is the idea that death has a plan for Harry that goes beyond what Dumbledore or anyone else expected. It could be that death wants to use Harry to balance the magical world in a different way. So, Harry might be led to discover ancient magic that is related to life and death, and he has to decide how to use it. This could involve making alliances with creatures that are associated with death, like thestrals or dementors in a different context.
A plot could be that Harry and Hermione are the only ones who can reverse the effects of a dark curse that is slowly killing all wizards. As Masters of Death, they must travel to the underworld and bargain with Death itself to get the cure. Along the way, they face many trials and learn more about the true nature of life and death.
Yes, there are some out there. You can start by looking on popular fanfiction websites like FanFiction.net or Archive of Our Own. Just search for the specific tags 'Harry Potter', 'Master of Death', and 'Riddick' to find relevant stories. Some might combine the magic and lore from Harry Potter with the unique and gritty world of Riddick in really creative ways.
One interesting plot could be the different ways characters' deaths impact the wizarding world's power balance. For example, if a key member of the Order of the Phoenix died, it might lead to a shift in the fight against Voldemort.
One interesting plot could be that the main character, who has assassin skills, is secretly protecting Hogwarts from a new and unknown dark threat that the regular wizards can't detect easily. They use their unique combat skills along with magic to keep the school safe.
One interesting plot could be a character using arithmancy to predict the return of a dark force. They might discover hidden patterns in numbers related to past dark events and use that knowledge to try and prevent a new threat.
One interesting plot could be Harry discovering a new, hidden magical ability that was not part of the original books. For example, the power to communicate with magical creatures on a deeper level. Another plot might involve Harry traveling to a different magical dimension where the rules of magic are completely different. He would have to adapt and use his skills in new ways.
Maybe in the fanfiction, Harry becomes the master of alchemy and uses it to create magical potions with extraordinary powers. For example, he might create a potion that can temporarily give students the ability to speak to animals, which leads to all kinds of adventures as they communicate with the magical creatures around Hogwarts.