I sort of went crazy with this headcanon. I wanted to do a story test based on random scenes with doodles ;_;. Based on one of my older stuff here that I did on tumblr [link]
Anyway, it's just a rough, but basically, something happened to the necklace Merida's mother gave her from their family heirloom...and somehow Jack got it lost or destroyed. So out of pride and anger, Merida breaks his staff and turns him into a polar bear (though she didn't know he was going to turn into a bear). And like the movie says, mend the bond torn by pride. Merida and Jack get close, and she fixes his staff somehow in the end before losing him, carving her and their friends around the bark that was split.
Honestly, there isn't much HP AU of Jarida, and I'm sort of concern of that :/. So, i guess this is my tribute to change that ^^. Again, sorry for the sucky art :/.
Tumblr post can be found here [link]