Well, he might gain superhuman strength and speed. He could also have the ability to influence minds, which would be a huge advantage. His magical abilities might be enhanced or changed in some way too. And he would probably have to deal with the thirst for blood, which could create a lot of internal conflict.
In such a fanfiction, Harry might gain enhanced physical abilities like super strength and speed. He could also have new magical powers related to his vampiric nature. For example, he might be able to hypnotize his enemies. His relationships with his friends would be severely tested. Hermione might try to find a way to reverse his vampirism while Ron could be initially afraid of him.
In 'harry becomes lord potter at 7 fanfiction', Harry is the main character, but there could be other important characters too. Maybe there are some members of the Potter family's old allies who come forward to help Harry. For example, the Longbottoms could be important as they have a long - standing relationship with the Potters. And then there might be some antagonists, like the Malfoys, who could be envious or try to undermine Harry because of his new title.
In fanfiction, if Harry Potter becomes Lord, he might gain a great deal of power and influence. He could use this new status to reform the wizarding world. For example, he could change the way Hogwarts is run, introduce new magical studies, or even restructure the Ministry of Magic to be more just and efficient.
Ron is also there. He could be Harry's right - hand man in some adventures related to his lordship. For example, when Harry has to deal with some dark wizards threatening his lands, Ron might be by his side, using his Weasley - family - taught magic skills.
Well, he might have to deal with new powers and instincts. He could gain super strength and speed like the vampires in Twilight. Maybe he'd struggle with his new thirst for blood while still holding onto his wizarding values. Also, his relationships at Hogwarts would change drastically as he tries to hide his new vampiric nature from his friends.
Well, he might gain a lot of power and influence within the wizarding world. He could use his new position to make changes in the way pure - blood families operate. For example, he could try to break down the traditional pure - blood elitism and promote more equality among wizards and witches, just like he always stands for justice.
Maybe in the fanfiction, as Lord Potter, Harry discovers ancient Potter family magic. This newfound magic could give him an edge in his fight against Voldemort. For example, he might find a spell that can protect Hogwarts in a more powerful way than the existing protective enchantments.