Well, it could be a character created by the fanfiction writer, perhaps a powerful mage who emerges from a long - forgotten land and claims god - like powers. This new god might bring a new set of rules and magic to the already complex world of Westeros.
Perhaps a young knight who is given a lordship as a reward for his heroism in a great battle. He is inexperienced in ruling but has a strong sense of justice. He has to learn quickly how to manage his lands, deal with political intrigue, and protect his people from bandits and rival lords. He is also a bit of a romantic, and his love interest could be a lady from a neighboring house, which adds another layer of drama to his story.
Maybe it's a former soldier who has shown great courage during a battle. He could have been the one to hold the line at Moat Cailin during a crucial fight, and in recognition of his valor, he's made the new lord. His military experience would be a great asset in ruling the area.
One impact could be on the religious beliefs of the characters. If a new god appears, existing religions might face challenges. For example, the Faith of the Seven could see a decline in followers as people turn to this new deity.
The desolate and harsh landscapes of God of War could be blended with the diverse regions of Westeros. For instance, the frozen wastelands where the White Walkers roam could be combined with the ice - covered areas in God of War. This would create a more extreme and dangerous environment for the characters.
A 'God of War' and 'Game of Thrones' fanfiction might feature a crossover of their mythologies. The gods in 'God of War' could interact with the Seven in Westeros. For example, Zeus could have some sort of encounter with the High Sparrow. Kratos might also have a unique perspective on the power struggles in the Seven Kingdoms, having dealt with his own power - hungry gods in his world.
In a 'God Naruto Game of Thrones' fanfiction, Naruto's character would bring a whole new dynamic. His journey to become Hokage in his own world has made him strong - willed and determined. In the Game of Thrones setting, he might view the Iron Throne as something similar to being Hokage. However, the complex web of relationships and betrayals in Westeros would be a huge challenge for him. He'd have to navigate through the schemes of Cersei, Littlefinger, and others while also dealing with the threat of the White Walkers if the story takes place during that time period.
The Mother. In the existing lore, she is a major figure. In fanfiction, she could be more actively involved in the events of Westeros. She could be a guiding force, using her powers to heal the sick and wounded, and trying to prevent the bloodshed that is so common in the Game of Thrones world.
Perhaps it could be a character like Bran Stark. He has the power of the Three - Eyed Raven, which gives him access to a vast amount of knowledge and some control over time and events. It's not a far stretch to think that he could develop into a Master of Death in a fanfiction.
One idea could be a new lord who is a long - lost heir to a powerful but fallen house. He starts from nothing, gathering a small group of loyal followers, some outcasts and misfits. He uses his wits and new - found knowledge of forgotten battle tactics to slowly rise in power. He might form an alliance with a group of local peasants who are tired of being oppressed by the existing lords. Through their combined efforts, they start to build a new, more just community which catches the attention of the greater powers in Westeros.
There could be a group of main characters. One could be an old maester who has seen many things during the previous era and now serves as a mentor to the younger generation. A second could be a wildling who has decided to integrate into Westeros society but faces many challenges. And a third could be a young noblewoman who is disillusioned with the traditional role of women in Westeros and is fighting for more equality. Together, they could be involved in all sorts of adventures and political intrigue in the new era of 'Game of Thrones'.