When a sickly young girl suddenly becomes obsessed with inventing new things, her family and friends are all puzzled. What has gotten into Main? they wondered, never dreaming that the answer is not a What but a Who: Urano Motosu, a book-loving apprentice librarian who died in an earthquake in Japan who somehow found herself in Mains body! And since Mains world is still in a medieval stage, where books can only be owned by the elite, the new Main intends to do everything she can bring her beloved books to the masses in the time she has left. Unfortunately, that may not be very long, as Mains body is still failing, and she may only have a short time left to achieve her lofty goals in Ascendance of a Bookworm!