Nico di Angelo has a strong connection to the Underworld, so he's a prime candidate. He can already communicate with the dead and has some control over the shadows, which are related to death in a way. In fanfiction, he could be further developed to become the Master of Death, perhaps by making a deal with Hades or finding a hidden power within himself.
In Percy Jackson fanfiction, the 'Master of Death' could refer to a character who has control over death in some way. Maybe they can cheat death, like Voldemort in Harry Potter who was after the Elder Wand to become the Master of Death. In the Percy Jackson universe, it could be a demigod who has some special power over the Underworld, perhaps being able to bring back the dead or prevent deaths that are fated. It's a really interesting concept that fanfiction writers can play around with to create unique and exciting stories.
Annabeth could be one of his main allies. She is smart and would help Percy understand the more complex aspects of his role as Horseman of Death. Grover might also be there for him, using his nature - related powers to help Percy in places where the power of death interacts with the natural world.
Well, in some Percy Jackson fanfiction, there might be other characters who are made to be the master of water. Maybe a new character is introduced who has some unique ability related to water that surpasses Percy's. However, usually, Percy is the main character associated with water powers because of his heritage. He can summon water, control its currents, and even communicate with water - based creatures. So, in most cases, when we think of the master of water in Percy Jackson fanfiction, Percy comes to mind first.
It could be an ancient and powerful Titan who escaped from Tartarus when the Doors of Death started to malfunction. This Titan wants to keep the doors open to bring back all the old enemies of the gods and take over the world again.
Well, sometimes in fanfiction, his brother might be a mortal who discovers his demigod heritage later. This could add an interesting twist to the story as he has to adapt to the world of gods and monsters. Or it could be a long - lost half - brother from a different camp, like a son of Poseidon from another part of the world who was hidden away for some reason.
One possible plot could be Percy being chosen as the Horseman of Death due to some ancient prophecy. He might have to travel to the Underworld more often and deal with the spirits there in a new way. Maybe he has to collect the souls of those who are supposed to die but are being held back by dark magic.
Another option could be a mortal martial arts master who unknowingly stumbles upon Percy. The mortal is a master of a rare and ancient form of martial arts. At first, he is hesitant to teach Percy because he senses something different about him. But as he gets to know Percy better, he realizes Percy's good heart and decides to train him. This would add an interesting dynamic as Percy has to balance his demigod life with his training under a mortal.
A powerful Titan who has escaped from Tartarus and wants to disrupt the Hunt could be an antagonist. They might see the Hunt as a threat to their plans for chaos. Another could be a rogue demigod who has turned against the Hunt and is now working for their own selfish gains, perhaps trying to steal the Hunt's magic weapons.
It could be an ancient shinobi who has mastered some kind of death - related jutsu and has ascended to a higher state of being. This shinobi might have been forgotten in the history of the ninja world.
Another common opponent could be other demigods from different cabins. For instance, a child of Ares who might have a more aggressive and straightforward fighting style compared to Percy. This would create an interesting dynamic as they have different powers and personalities but are still on the same side in the general scheme of things.