BAKEMONOGATARI (manga) 16

"Newcomers and existing fans alike will enjoy diving into the world of Monogatari and meeting the delightful cast of characters. If you're yet to experience this series in any form then this is the perfect time to climb aboard!"
- Anime UK News

One day, high-school student Koyomi Araragi catches a girl named Hitagi Senjougahara when she trips. But -- much to his surprise -- she doesn't weigh anything. At all. She says an encounter with a so-called "crab" took away all her weight...
Monsters have been here since the beginning.
Always. Everywhere.