Rainbow Dash spends extended amounts of time with Twilight at the library. Being even lazier than usual, she starts to exercise less for the sake of reading. At the same time, her intake of delicious sugary snacks increases, but not without the help of the friendly librarian.
Why is the unicorn letting her eat so much? And why doesn't the pegasus really mind?
Note: Twidash fic, with chubby dash. Somewhat suggestive. Not over/forced feeding.