Well, a cool plot idea might be Arya establishing a new code of laws in the North. Since she has seen so much of the world and different ways of life, she could bring in new ideas that are more fair and just for all. Also, she could be involved in a story where she has to make an alliance with an unexpected group, like a group of former enemies of the Starks who now see her as a different kind of leader. And she may have to deal with some sort of magical or supernatural element that is starting to affect the North, using her wits and any knowledge she has gained on her travels.
One plot idea could be Arya having to deal with political intrigue in the North. Maybe there are rival lords who don't fully accept her as Queen and she has to outwit them. Another could be Arya facing an external threat like a new wildling uprising, but she uses her unique skills to handle it. And perhaps she could be on a quest to find a long - lost Stark heirloom that is said to have the power to unite the North even more firmly under her rule.
An interesting plot could be Arya's journey to strengthen the North's defenses. She could start by training a new generation of warriors, teaching them her unique combat skills. There might be a sub - plot where she discovers a traitor within her own court who is secretly working for an outside force. To counter this, she travels to different parts of the North to gather support and resources. Along the way, she meets old friends and makes new allies, all while trying to prove that she is a worthy Queen of the North. She could also face challenges related to the changing climate in the North and how it affects the people and their way of life.
As Queen of the North, Arya's character would transform significantly. Her wild and independent streak would still be there, but she'd learn to channel it in a more productive way. She'd start to understand the importance of traditions and how they can be used to unite the people. Her relationship with power would be complex. On one hand, she'd use it to protect the North, but on the other, she'd be cautious not to let it corrupt her. She'd develop a more regal presence, but still keep her roots as a Stark. Her skills as a spy and assassin would be used in more strategic ways, like uncovering plots against the North and eliminating threats without causing unnecessary chaos. And she'd have to learn to balance her personal desires with the needs of her kingdom.
One idea could be Arya traveling back to the time before her family's downfall. She could use her skills to prevent certain events from happening, like Ned Stark's execution. Maybe she'd change the course of battles by secretly assassinating key enemies.
One plot idea could be Arya, in disguise, getting close to Tywin as a servant in King's Landing. She could overhear his plans and use that knowledge to try and undermine the Lannisters from within. Another could be a scenario where Tywin discovers Arya's true identity but decides to keep her alive for some strategic reason, perhaps to use her as a bargaining chip against the Starks. And a third idea might be a story set in an alternate universe where Arya and Tywin form an unlikely alliance against a common, greater threat, like a White Walker invasion in the south before the events at the Wall.
One plot idea could be Arya and Jon teaming up to uncover a long - hidden family secret. Maybe there's a lost Stark heirloom that has some sort of power, and they have to go on a quest to find it. Another idea is that they are both sent on a diplomatic mission to an unfriendly kingdom, and they have to use their unique skills - Arya's stealth and Jon's leadership - to succeed.
One plot idea could be that Arya and Aegon meet during their travels. Aegon, with his claim to the Iron Throne, is in need of a skilled ally like Arya. She could help him in his political maneuverings in a way that no one else can, using her skills of disguise and stealth. Another could be a story where they are forced to team up against a common enemy, like a new threat rising in the Seven Kingdoms that neither the Starks nor the Targaryens can face alone. They start off distrustful of each other but gradually come to respect and rely on one another.
One idea could be that the male OC is a foreign noble who comes to Winterfell. He has unique fighting skills and Arya is intrigued. They start training together in secret, and as they do, a deep bond forms. This could lead to them going on adventures together, facing threats to the North.
One interesting plot point could be how Arya uses her unique skills learned during her travels to defend Winterfell. For example, her skills in stealth and assassination might be used to uncover and thwart hidden threats within the castle.
One interesting plotline could be Arya and the Hound facing a new and powerful enemy together. Maybe they encounter a group of bandits with a cruel leader, and they have to use their combined skills to defeat them.
One major challenge would be political. There would be many lords in the North who might not accept her rule easily. They could be traditionalists who think a woman shouldn't be in charge. Arya would have to prove herself through her actions and leadership skills.
A possible plot is that a spell gone wrong makes Queen's music the only thing that can calm a dangerous magical creature. Hermione, being the clever witch she is, uses her love for Queen to figure out how to tame the creature and in the process, she also uncovers a long - lost magical connection between Queen's music and ancient wizarding magic.