Just a guess, but they're probably destined enemies because Merida's a Scot/Celt and Hiccup's a Viking. The two groups rarely ever got along - even in the movie, Brave, the Lords occasionally mention Vikings as enemies (MacGuffin's boast about his son was that he fought against Viking longships and vanquished 2,000 foes - presumably Vikings).
But that's okay. Individually, the two can break tradition and be friends. They're good at that.
This is awesome! I love the colors and it's so amazing and right! As in, they look right! Like, really, really awesome! I love it 8D Dude, I just noticed it looks like Jack has sparkles flying out of him, LIKE NYAN CAT Sorry, had to say it C3