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1) A Waifu Killer is someone who cosplays your favorite character preferable female anime character and you don't like the person for cosplaying the character you like.

2) Someone you dislikes who cosplays a favorite character of yours and you really don't want to see them as said character.
1) Man, why did Antonio cosplay Hestia, what a waifu killer!

2) She had to cosplay three of my favorite characters, damn waifu killer!
by Julia Lenna September 21, 2016
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