You can start by looking on fanfiction.net. It has a large collection of fanfics from various fandoms, including many about Boromir.
I'm not sure if there is such a specific fanfic. Fanfics cover a wide range of themes and scenarios, but this particular one seems rather unorthodox. It might exist in some corner of the vast fanfic universe, but it's not a common or widely known concept.
One popular 'boromir lives fanfic' might be 'The Redemption of Boromir'. In this fic, Boromir survives the battle and goes on a journey of self - discovery and atonement. He tries to make up for his past mistakes and becomes a key figure in the fight against the encroaching darkness.
One great Boromir fanfic is 'The Redemption of Boromir'. It delves into his internal struggle after being tempted by the Ring. Another is 'Boromir's Path', which focuses on his journey before arriving in Rivendell.
One common theme is redemption. Since Boromir's character in the original story had some flaws and made mistakes, in these fanfics where he lives, he often gets the chance to redeem himself. For example, he might make amends for his actions regarding the One Ring.
One great 'boromir x reader fanfic' is 'The Unseen Bond'. It beautifully captures the essence of Boromir's character and his relationship with the reader. The story is filled with adventure and emotional depth.
A good 'boromir x reader fanfic' should have a strong understanding of Boromir's character. His noble yet flawed nature needs to be accurately portrayed. For example, his pride and his loyalty to Gondor are important aspects.
I'm not sure where to find the '1318171 fanfic' as the name doesn't give any obvious hints. You could try searching for it on popular fanfic platforms like Archive of Our Own or FanFiction.net.
You can try looking on fanfic - specific websites like Archive of Our Own (AO3) or FanFiction.net. These platforms usually have a wide variety of fanfics, and you can search for '25 21 fanfic' in their search bars.
Boromir might develop a sense of wonder. Earth has so many different cultures, landscapes, and technologies. This exposure could make him less rigid in his thinking. He could start to question the way things were in Middle - earth and consider new ways of living. He might see how different races interact here in a more peaceful way compared to the tensions in his own world and strive to bring that back to Middle - earth if he ever returns.
First, study Boromir's character. Know his virtues like his loyalty to Gondor and his family, and his flaws such as his susceptibility to the power of the Ring. Then, create an OC that can interact meaningfully with him. For example, if your OC is a scholar, they can debate with Boromir about the history and power of the Ring.