Crossposted from fanfiction.net!

A mountain king... A princess of night... The stars kiss their meeting, and their worlds won't be the same.
When Luna finds a new door in the dream realm leading to the dreams of the King of Monsters, Asgore, she befriends him almost immediately. Over time they grow close, but when the Legion strikes in Equestria, Luna turns to him for help.

The story spans Season 9 of MLP:FiM and happens before Frisk's fall in Undertale.

Rating now updated to T and the Gore tag added because of a character's described injuries in chapter 6. Not sure the tag itself is needed, but the rating definitely needs to be Teen.