The Knights of the Epic Brave Dragons is an EU (Extended Universe) focusing on Hiccup and Merida. This EU suggests that Mary Katherine from Epic and Justin from Justin and the Knights of Valour are supposedly their children. Because it is not canon, ideas for this EU are shown through fanfiction, fanart, and other fan-made works. This EU is considered to be an extension of the Mericcup pairing.
About the EU
This universe was created as an "equal-opposite reaction" to the EU Frozen Tangled Guardians, which focused on the possibility of a Jackunzel family with Elsa and Anna from Frozen as their children. Mary Katherine' hazelnut hair and cynical personality are traits similar to Hiccup, but shows a more headstrong, compulsive nature like Merida. Justin has a lanky, out-of-place physique and incompetence in a warrior lifestyle much like Hiccup at his age, but has the red hair and cultural similarities to Merida. Though not as popular as Frozen Tangled Guardians, this EU has slowly grown a following.