I recommend 'Robb Stark: The Lost Legacy'. This fanfiction focuses on an alternate timeline where Robb survives. It's interesting as it explores how he would have changed the course of the story. It has some great character development and interactions with other key characters from the series.
The relationship between Robb and Talisa in fanfiction can also be a source of great emotional drama. Their love could be tested by war, betrayal, and family obligations. Fanwriters might write about their private moments of joy and sorrow, how they comforted each other during difficult times, and how their love endured or, in some cases, tragically ended.
Another reason is that Robb Stark's story ended tragically in the original series. Fans are drawn to fanfiction as a way to rewrite his story, give him a better ending, or just see different interpretations of his character. It allows for a lot of creativity and speculation among fans.
One great 'Game of Thrones Robb Stark OC fanfiction' is 'The Stark Heir'. It follows an original character who becomes an important ally to Robb Stark. The story has great character development and exciting battle scenes.
One possible plot could be that Robb Stark manages to avoid the Red Wedding trap. Maybe he receives a tip - off from an unexpected source, like a disgruntled Frey servant. With this knowledge, he could turn the tables on his enemies. He might use his military strategy skills to ambush the Freys instead, and this could lead to a major shift in the power dynamics in the North, with Robb emerging as an even stronger leader.
It could change it a great deal. In the original story, Robb's actions regarding the Freys led to the Red Wedding. But if he married a Frey, it would mean no Red Wedding. This would keep Robb alive and his army intact. It could also change the power dynamics in Westeros as the Stark - Frey alliance would be very strong.
First, do your research on Robb Stark's character. Know his traits, his goals, and his relationships in the original series. Then, create your original character with a clear backstory, personality, and motivation. Make sure the OC's story can fit into the world of Game of Thrones. For example, if your OC is a warrior, think about where they learned their skills and why they would side with Robb Stark.
In a fanfiction, Robb Stark's twin brother might be a seer. He has visions of the future that are different from Bran's. While Robb is fighting his wars, his twin is trying to use his gift to prevent disasters. For example, he might see the Red Wedding in advance and try to warn Robb. However, due to the chaos of the war and disbelief from others, his warnings go unheeded. This could lead to a story full of regret and a new determination to avenge Robb's death and change the fate of the Stark family.
Robb Stark would likely become more cautious. After narrowly escaping death at the Red Wedding, he would know that his enemies are ruthless. This would make him more calculating in his military campaigns and political moves. He might be less trusting, especially of those who have shown signs of betrayal in the past.
I really like 'Brothers in the North'. In this fanfiction, Robb and Jon are depicted as having a very strong bond. It shows how they might have worked together to face the various threats in Westeros. The characterizations are well - done, and it has an interesting plot that keeps you hooked from start to finish.