Pairing: Kagome Higurashi/Inuyasha, Rin/Sesshoumaru
Fic Title: Love's Smirking Revenge
Rating/Warning(s): MA (sex, language, violence)
Genre: Crime, Mystery, Romance
WIP?: No - 200,904 words (41 chapters)
Why This Must Be Read: I have yet to meet a fanfic writer who can write a good, solid, absolutely engaging mystery - so this story was a wonderful surprise. Written like an old-school hard-boiled detective novel, Langus sweeps us into a modern-day world while keeping the canon mythology that makes Inuyasha so interesting and complex. There are multiple storylines which weave together in compelling and sometimes surprising ways, and enough action to keep you on the edge of your seat. There is also plenty of hot romance between canon pairings - so if that's your thing, then this is definitely the story for you :P
Just when you think you know whodunnit, the author throws out a final shocking twist - one that reverberates through the entirety of the story, making you want to go back and read it all over again from the beginning. Another nice touch is that every character has closure, not just the main pairing - a rarity for sprawling fic with multiple story arcs. This is a definite don't miss!
ETA: Edited 11/10/12 to reflect the story's status as complete & to tweak the final recommendation.