If, for no apparent reason, Horo suddenly turns out to be widowed, is she free to be chosen again?
Well, I guess best things in life are the one's you can't get, anyway. Let's leave it like that.
My second waifu has been chosen before, but since it has been stated that previous second waifus are void, I'll go ahead and claim her for myself!
Second waifu: Illyasviel von Einzbern.
Reasons: DFC, white hair, red eyes, childish innocence, a little snobby, cheerful, high nobility, outstanding skills in handling magical energy and she's german, so I could actually talk with her - unlike with my first waifu.