A deity or other such powerful being asks you to become its agent on earth, if you choose to accept The deity gives the character an unusual pet as a gift. (work with your DM to determine details)
Divorce: During your adolescence your parents split up and you were forced to chose which parent to live with (Work with your DM to detirmine the details)
While foraging or hunting for food, you have an encounter with a trapped predatory beast. Instead of slaying it, you free it. The freed beast disappears. Later, you are trapped by a falling log. The same beast reappears, aiding and freeing you.
a strange pale woman gave them an ornate box sealed with wax and hoarsely whispers "It's up to you now, keep it safe, keep it from ... them." The woman droped dead at their feet with a dagger in her back