Perhaps a plot where Talion and Celebrimbor are transported to a different time or dimension. In this new place, they find that the power of Sauron is even more menacing or takes on a different form. They have to quickly adapt and find allies in this strange new world. They might also discover that their connection to each other is somehow linked to the very fabric of this new dimension. This could lead to a series of adventures where they not only fight the external threats but also have to deal with internal doubts about their partnership.
You could write a fanfiction where Talion travels to different regions not explored in the game. He might encounter new cultures and races, some friendly and some hostile. This could lead to him having to adapt his combat and survival skills. And perhaps he discovers a long - lost artifact that has the power to either greatly enhance his abilities or put him in a dangerous position as others seek to take it from him.
Talion could develop a greater sense of self - identity. Initially, he was somewhat defined by his revenge mission, but in fanfiction, he might start to see a future beyond that. He could become more of a leader, guiding others in the fight against Sauron. For Celebrimbor, he could regain more of his former self - confidence. As he continues to fight alongside Talion, he might remember more of his past glories and use that knowledge to be more assertive in their battles. He could also become more empathetic towards Talion's human side.
One plot idea could be that Talion and Shelob form an uneasy alliance against a greater evil in Mordor. They start to understand each other's motives and powers more deeply as they fight side by side.
One interesting storyline could be Talion and Shelob forming an unlikely alliance against a greater evil in Mordor. They might combine their unique powers, Talion's combat skills and Shelob's web - spinning and venomous attacks, to take on powerful orc warlords.
The contrast between them. Talion is a human with a complex past, while Celebrimbor is an ancient elf. Their different natures make their interactions fascinating.
One idea could be Bruz's backstory before he became a part of the story in the game. Maybe he had a family or a different life goal that was shattered by the events leading to the war. Another could be a 'what if' scenario where Bruz didn't turn evil and instead became a key ally in the fight against the real enemies.
Another plot could focus on an orc's rise to power within the Uruk - hai hierarchy. This orc could be different from the others, having unique skills or a different way of thinking. He has to outwit his rivals, make strategic alliances, and deal with the power - hungry captains who don't want to see him succeed.
One idea could be exploring an alternate timeline where the main characters have different allegiances. For example, Sasuke could side with Orochimaru permanently and Naruto has to find a way to bring him back without fighting. Another could be a story where the Akatsuki are actually working for a greater good that was misinterpreted, and Naruto teams up with them to fight a common enemy.
One common theme is the struggle with power. Talion has the power of the ring, and many fanfictions explore how he grapples with it. Another theme is redemption. Given his actions in the game, some fanfictions focus on whether he can be redeemed.
One great 'Shadow of War Talion crossover fanfiction' I read had Talion teaming up with characters from another fantasy realm. It was really exciting as it explored Talion's character in a new setting. The author did a great job of keeping his essence intact while adding new elements from the crossover.