A strange woman gives you an ornate box sealed with wax and hoarsely whispers "It's up to you now, keep it safe, keep it from ... them." It is not until the woman drops dead at the character's feet that the dagger in her back becomes obvious.
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.
Social. A social enemy might be a personal rival, an idealogy, or a cultural trait. Its an enemy tied to interactions with others, they may have trouble fitting in, be a social outcast, not identify with their culture, or be wanted but their own kind.