I really like 'Edward Elric: Unforeseen Bonds'. In this fanfic, the relationship between the reader and Edward develops in a very natural way. It starts from a chance encounter and gradually blossoms into a deep connection. There are a lot of emotional moments that make it a great read.
There's also 'The Alchemist and the Reader'. This fanfic is unique because it delves deep into the world of alchemy while also exploring the relationship between the reader and Edward. It has a complex plot that keeps you hooked from start to finish. Edward's growth as a character within the relationship is really well - written.