As a Swordsage//Ninja you might also hail from the Jade Islands, and have consorted with their flavour of yokai "fey". Or be a native Krevbornite and have learned your invisibility tricks from your fey friends.
Either would be a terrific fit in the setting.
And yes, fey in Krevborna are not nice. Maybe not Evil as per the alignment, but at least dubious.