The followers of an unheard-of-god from another land followed omens that led them to you. The omens indicate that you are to be the mate of an avatar (earthly incarnation) of their god. You disagree but are still harassed by the god's followers.
Martial training: In adolescence you trained with the weapons of your people and learnt how to use them proficiently (work with your DM to determine details)
You were abducted by otherworldly beings (planar, fey, fiend or celestial) Moments later, you reappear, but has physically aged 1d10+10 years, has no memories of that lost time, and has not mentally aged even a minute.