There is a rumor of a legend of a story in Equestria. Of a creature, older than can be told, that can bridge the most painful gap. The gap between two hearts that long to know oneness. To clear away the barriers that stop love from fully blossoming.

Big Macintosh knows the pain of love that cannot be, without subjecting his lover to suffering and eventual existential torment that would consume her. So he undertakes the journey, to walk the path of the hero. He need not wait for the middle of the journey of his life. He will strive for his happiness. And Smarty-Pants' happiness as well.

(Yes, this is VERY much inspired by Dante's "Inferno" and "Purgatorio." As it goes on, you'll see the connections between broad elements and know why I didn't need to add "Paradiso.")