Peter Pettigew and Bellatrix Lestrange, how he became a Death Eater due to his love (unknown to his friends naturally) of Bellatrix and envision this with BDSM envolved to some extent - set in school years to DH.
Ron Weasley as a Death Eater, set in 4th year after him falling out with Harry over the Goblet of Fire pulling his name out so AU naturally and can bash him or show him however you want.