The fact that it allows for a new perspective. With an original character, we can explore aspects of Elrohir's life and world that might not be covered in the original works. For example, an OC could be from a different culture or have a unique ability that leads to new adventures and interactions with Elrohir.
One common theme is friendship. Since the original characters (OCs) are often inserted into the world with Elladan and Elrohir, the development of friendship between them is a big part. For example, the OC might start as a stranger and gradually become a trusted ally.
Another one is 'A Bond with Elrohir'. Here, the OC is a healer who forms a special bond with Elrohir. The story is filled with emotional moments and great dialogue. It really delves deep into the personalities of both characters, making it a very engaging read.
Another interesting one is 'Among the Elves: Elladan, Elrohir and OC'. This story dives deep into the elven culture and how the OC adapts to it while being in the company of Elladan and Elrohir. It shows their daily lives, their training, and how they interact with other elves. The descriptions of the elven settings are really vivid, making you feel like you're right there in Middle - earth.
One interesting story could be about their early adventures in the forest near Rivendell. Maybe they discover a hidden glade filled with magical creatures. Another could be about their first attempts at learning elvish archery from their father, Elrond.
In the fanfiction, perhaps Elladan and Elrohir would be intrigued by the Dwarves' craftsmanship. The Dwarves, in turn, might be impressed by the Elves' grace and magic. They could end up sharing stories around a campfire, forging an unlikely friendship.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). There are often many Tolkien - related fanfictions there, and you can specifically search for ones about Elladan and Elrohir as babies. Another place could be some Tolkien - focused forums, where fans might share their own written works or recommend good fanfictions.
In The OC fanfiction, 'Ryan Blind' could be a character that serves various purposes. It might be a character who represents a different social class or has a particular skill set that the author wants to explore. For example, if the fanfiction delves into the world of art, Ryan Blind could be a blind artist who has a unique perspective on life. He could also be a character used to create drama or conflict, like being in love with Marissa but facing some obstacle due to his blindness or some other aspect of his character.