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Goodreads asked E.G. Manetti:

Who is your favorite fictional couple, and why?

E.G. Manetti Other than Lucius & Lilian from The Twelve Systems Chronicles?

There are several. Off the top of my head (I'm sure I'm missing some):

Adam & Mercy from the Mercy Thompson series (Patricia Briggs)
Charles & Anna from the Alpha and Omega series (Patricia Briggs)
Eve and Roarke from the In Death Series (JD Robb)
Phedre and Jocelyn from Kushiel's Dart (Jacqueline Carey)

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