What might be the plot of a 'harry potter is a big brother fanfiction'?

Maybe Harry would find out about his relation to Merlin through some magical artifact or prophecy. Then they could team up to fight a greater evil that threatens both their worlds.

One possible plot could be that they discover their relation early on. Harry, instead of being alone, has an older brother figure in Snape. Snape might then be more protective of Harry from the start and try to shield him from the dangers at Hogwarts in a more direct way.

In this type of fanfiction, a possible plot is that the Death Eaters and the Order of the Phoenix members are forced to live together in a 'Big Brother' style house. They have to follow certain rules set by the magic of the house. There are tasks related to both dark and light magic. The characters have to balance their own beliefs and goals while also trying to win the overall competition. This creates a lot of tension and interesting character interactions as they all have very different motives.

The plot could involve Harry being a reincarnation of Anubis. He might start to have strange dreams and visions related to his past life as the Egyptian god. As he tries to understand these, he discovers that his powers as Anubis are starting to surface. This could lead to him having to protect the wizarding world from a new kind of threat that only his combined powers can defeat.

Maybe Harry Potter and his friends have to follow Colonello's orders for some mission in the wizarding world.

Maybe Gandalf appears in the wizarding world of Harry Potter and helps him to defeat Voldemort. He could use his powerful magic that is different from what they have in Hogwarts.

Well, the plot might involve Voldemort's brother being raised in a different part of the wizarding world, completely unaware of his relation to Voldemort. But then, through a series of events, he finds out. He might then struggle with the knowledge that his brother is the most feared dark wizard. He could try to redeem Voldemort at first, but when that fails, he devotes himself to helping Harry Potter and his friends defeat Voldemort. He might have some unique magical abilities that prove crucial in the final battle.

In this fanfiction, perhaps the Japanese god has a prophecy about Harry. The plot might be that Harry is transported to a realm where Japanese mythology and magic coexist. There, he has to prove himself worthy of the god's power. He could learn new forms of magic, make new friends from the Japanese mythological creatures, and at the same time, figure out how to use this new power to protect his own world. For instance, he might have to face a dark wizard who has also tapped into some of the power of the Japanese mythological world, and Harry's newfound connection to the god gives him an edge in the battle.

Well, one possible plot could be that Harry uses his magic to combat various threats to the country that normal politicians can't handle. Like using spells to stop terrorist attacks or natural disasters. He might also have to hide his magic from the public while still using it for the greater good.

One possible plot could be that Harry discovers a hidden connection between his wizarding world and the world of vampires. Dracula, for some reason, sees potential in Harry and decides to make him his'mate', which could mean an apprentice or a partner in some dark magic deeds. Harry, initially reluctant, gets drawn into Dracula's world as he realizes there are secrets about his own magic that Dracula can help him uncover.