After a mighty storm has passed, You discover a old waterlogged chest, sealed with chains and weighted with stones. You find drowned form of a young animal. Suddenly, the creature's eyes open you have acquired an unusual pet.
A vicious animal attacks you on a moonlit night. Friends drive the beast off, but you discover that you've been cursed with lycanthropy, to become a similar beast under the full moon. (work with your DM to determine details)
When you become an adult you learn to used a weapon (of your choice) appropriate for your culture and social standing. (work with your DM to determine details)