megamultiverse and somehow intervene in events although without compromising the integrity of each narrative as historical fiction, fantasy, sf etc. Trygve Yamamura, the hero of three detective novels, touches on fantasy in one short story.
Who are the mysterious characters of literature? Why did the Time Traveler's dinner guests include the Silent Man? Who was the man in grey that bought the Crystal Egg? Who was the young man that followed Jesus when he was arrested but ran away naked leaving his linen cloth behind?
DC Comics has a sort of supernatural Lone Ranger called the Phantom Stranger (see here) who appears when needed but disappears as quickly. He is an immortal, a neutral angel, the Wandering Jew, an immortal time traveler...speculative origins. The Stranger, if no one else, would be able to access Poul Anderson's immutable timelines.