Title: A song for two voices (starting with In your arms I shall not fear the night)
Fandom: The Heralds of Valdemar
Pairing: Canon pairings (Vanyel/Tylendel)
Categories: AU
Length: 350k and counting
Rating: T for canon-level violence
Author: swimmer963
Author's Summary: This is a rationalfic take on "The Last Herald-Mage", inspired by HPMOR and other works. Accessible regardless of whether you've read the original series. Though far from perfect, the characters are trying to do their best with the information, intelligence, and skills they have. Unfortunately, their enemies are also doing that, and sometimes even reasonable decisions can turn out badly.

Ashamed of him, Vanyel's father sends his disappointing son to live with his strict aunt, the Herald-Mage Savil. Although he knows things will change, Vanyel dramatically underestimates just how different his life is about to become. Sparks fly as he discovers both love and magic.

My comments: I don't often have the exquisite pleasure of recommending an actively updating fic in progress and holy shit, I think the author updates weekly. 

Anyways, I know it's hard to tell but I've had my head buried in Valdemar for a long time and once I'd hit the end of the available chapters I couldn't believe that 350k words and counting had garnered fewer than 200 comments. Suppose it's not a particularly popular fandom, and I can understand why - I love Mercedes Lackey's worldbuilding but she can get preachy and her villains are silly and moderately incompetent. This author remedies both of those flaws. Swimmer963 says that the series is a "rationalfic" inspired by Harry Potter and the Methods of Rationality, but the story's "rational" properties are subtle (apart from some gentle discussions of, I think, deontology vs utilitarianism and Hobbe's social contracts?), characters have realistic levels of knowledge and awareness. Also, Leareth is definitely more complex, more relatable, and more sinister in Swimmer963's incarnation (pun intended). 

Anyways, this is the longest and best Valdemar fic I've ever read.