Idea came to me after seeing this post on tumblr (link on profile). Ariel is named after the person who inspired Mabel. BTW, capitals make the world so much easy to understand.

The year was 1923 when the young Civer twins came back home to Gravity Falls from their boarding school. The twins were an adventurous duo, spending their summer slipping out of the cabin their family owned to explore the woods that surrounded the town.

That was why it was such a shock when the twins began avoiding the woods part way through the summer. They would seclude themselves in their attic room and drag one or both of their parents with them if they wished to travel the short road that led from their family's cabin to the town proper. They were always together and always on edge.

"There is something in the woods," the twins would reply when those that noticed the change asked.

As adults often do, the townspeople waved aside the ominous warnings as the overactive imagination of children. "Besides, it is for the best. There are all sorts of animals in the woods that would love to gobble up a pair of twelve year olds." That is what they told themselves...

Until the twins disappeared.

One morning, a short week before the twins had been scheduled to return to school, their mother came to their room to wake them for breakfast, only to discover two empty beds. The townspeople searched high and low, but while Ariel was discovered in a clearing just a short ways from the cabin, William was never found.

Aside from a nosebleed that had stopped prior to her being discovered, Ariel was unharmed. When she awoke and was questioned, the girl stated she remembered nothing of what happened.

As soon as Ariel was cleared, the family left Gravity Falls. The parents found a home in California, closer to where their now only child was attending school, though the kept in contact with a few people from their old town, just in case William ever reappeared.

The old Civer cabin remained untouched for years until Ariel's two sons moved in. As neither boy had seen what the cabin had looked like during their mother's time and Ariel had never gotten the chance to revisit the old house, no one ever noticed that some of the once normal windows on the cabin now boasted triangular designs. Specifically the one in the twins' room and the window seat William had always love to sit in to read.

The year was 2013 when the young Pines twins came to Gravity Falls to visit their great uncle Stan. The twins were an adventurous duo, spending their summer slipping out of the cabin that their great grandmother Ariel Pines née Civer had once lived in to explore the woods that surrounded the town.

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