The twins Dipper and Mabel enter a portal that leads them to an alternate universe where the twins' enemies are the good guys and where the twins are the bad guys instead. Chaos ensues when the twins meet their evil opposites in the alternate universe, and it's up to the good twins (And some of their familiar, yet new friends) to stop the bad twins from taking over Gravity Falls.

When Ryou Bakura receives a Vocaloid software, weird things start happening. It turns out to be the cause a certain turquoise-haired girl named Miku Hatsune, and she seems to hold immense power. Can Ryou protect her from others who wish to take her power?