In this fanfiction, the plot might revolve around Harry's struggle to balance Kreacher's teachings with the values of the wider wizarding world. He could face discrimination from other wizards who are suspicious of his upbringing. Meanwhile, Voldemort might see Harry as an even greater threat because he's been raised by Kreacher. Kreacher, being protective, tries to shield Harry from the Dark Lord, but Harry realizes he has to take a stand. This could lead to a series of battles and adventures where Harry has to prove himself not just as a wizard, but as a person with his own set of beliefs.
Kreacher is a very traditional character. His influence on Harry could mean that Harry is more into the old magic. He might be taught spells and incantations that are not commonly known in modern wizarding society. Also, Kreacher's loyalty to the Black family could make Harry more protective of the remaining members of the family and their heritage.
The plot could start with Harry escaping the Dursleys earlier than in the original. He then roams around, trying to find a place to belong. He might stumble upon some hidden magical secrets in the Muggle world that are related to his parents. As he grows, he starts to attract the attention of both good and bad wizards. Some might want to help him, while others see him as a threat because he's an unknown factor, not following the normal wizard upbringing.
The plot could start with Harry being found by a samurai clan. He'd grow up learning their ways. Then, when he discovers his magical heritage, he has to blend the two worlds. Maybe he uses samurai skills to fight dark wizards.
It would be a unique take on the Harry Potter story. Kreacher is a complex character. He could raise Harry in a way that emphasizes self - sufficiency and loyalty to a fault. Harry might not be as eager to jump into the fight against Voldemort as in the original story. Instead, he could be more focused on protecting his own little world created by Kreacher. Also, his magic could develop in a more unorthodox way due to Kreacher's unorthodox teaching methods.
It could be really interesting. Kreacher, being a rather complex and initially prejudiced house - elf, would raise Harry in a very different way from the Dursleys. Harry might grow up with a deep knowledge of the Black family secrets and traditions. He could also be more in tune with the wizarding world's darker elements from a young age.
In this fanfiction's plot, Harry's identity as the Boy Who Lived would be intertwined with his military upbringing. He could start a sort of 'wizarding army' within Hogwarts, recruiting students who are willing to fight against the dark forces. His training by soldiers would make him a natural leader in this regard. The story would then revolve around his efforts to build this army, face the opposition from some traditional wizards, and ultimately use this new force to defeat Voldemort in a more strategic and coordinated way.
The plot could start with Harry being born on a spaceship or a space colony. As he grows, he discovers his magical powers, which are different from those on Earth. He then gets a message or a sign that leads him to a quest. This quest might involve finding a lost magical object that has the power to save the space - wizarding community from a dark force. Along the way, he meets other magical beings from different parts of space and they form a team to complete the mission.
The plot could involve Harry using his magic in a more open way around the Dursleys. They might help him hide it from the wizarding world until he's old enough to go to Hogwarts. Then, at Hogwarts, he could be more focused on learning for the joy of it rather than as an escape from his horrible home life.
The plot might start with Harry being taken in by Pitch Black at a very young age. Then, he would be taught things that are not part of the normal Hogwarts curriculum. As he grows older, he might start to question the motives of Pitch Black. This could lead to a conflict between them, and Harry could decide to break away and find his own path in the wizarding world, perhaps with the goal of using his unique skills for good.
In fanfiction, Harry and Kreacher could be seen exploring the different terrains of Westeros. Maybe they stumble upon the Iron Islands. Kreacher could be fascinated by the Ironborn way of life while Harry tries to find a way to use their naval power for some greater good. Or they could end up in King's Landing and face the political intrigue there.