In some fanfics, like 'The Master of Death's Dominion', Harry uses his new status to become a benevolent dictator of sorts in the wizarding world, changing the political structure. In others such as 'Harry, the Reluctant Master of Death', he is hesitant to use his power and tries to hide it. And in 'Master of Death: A New Era', his being the Master of Death ushers in a new age of magic with different rules.
In crossover fanfics, the 'Harry Master of Death' concept often gets expanded. For example, in a crossover with the Star Wars universe, his mastery over death might be translated into an ability to resist the dark side's allure, which is related to death in a different way than in the Potter universe. He could use his power to save characters from the brink of death in a more 'Star Wars - y' way, like using the Force in conjunction with his magic.
In some fanfictions, it changes by giving Harry more direct control over life and death. For example, he can revive the dead or prevent people from dying in a way that was not possible in the original books.
In some fanfictions, it makes Harry more confident. Since he knows he's the master of death, he feels a sense of purpose and power that he didn't have before. This newfound confidence allows him to take on Voldemort more fearlessly.
It changes the power dynamics. In the original story, Harry is just a normal wizard with a special destiny. But when raised by Death, he may have access to powers beyond normal magic. He could be more in tune with the darker aspects of magic, like necromancy in a non - evil way. For example, he might be able to control or communicate with ghosts in a more profound way.
Well, in fanfics, Obscurial Harry often means a more unpredictable Harry. His power can be a wild card. For example, in some fanfics, it makes his battles against Voldemort more intense as he has this hidden, often uncontrollable power.
The 'Golden Boy' idea can also change Harry's relationships. Since he is seen as special, some characters might idolize him more. Others might be jealous of him. For instance, some Slytherins could be even more antagonistic towards him, while some Gryffindors might follow him blindly. This creates different power dynamics and social situations compared to the books.
In many fanfics, it completely changes Harry's identity perception. Instead of just being the Boy Who Lived, he now has this complex connection to Slytherin, which was considered the 'evil' house in the original. This can lead to different relationships with characters like Draco Malfoy. They might become allies instead of rivals in some fanfics.
In fanfics, as the 'Light Lord', Harry often becomes more confident. Since he has this special title and the associated powers, he feels more in control. For example, he may be more assertive in his decision - making compared to his canon self.
It adds a whole new layer of magic and relationships. In the regular Harry Potter series, werewolves are on the fringes, but with Hermione as a werewolf mate, it brings that part of the magical world closer to the main characters. For example, her friends might have to deal with werewolf politics now.
It often changes the relationships. For instance, he might be at odds with Dumbledore from the start. Since a dark pureblood upbringing could make him skeptical of Dumbledore's motives which are often seen as very 'light - side' in the original books.