Bakemonogatari (Manga) Volume 20 Av Nisioisin, Oh! Great

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.