Bakemonogatari tells the story of Koyomi Araragi, a third-grader who's almost human; in other words... He used to be a vampire!
The plot begins one day when he sees one of his classmates, Hitagi Senjougahara, fall down the stairs. He saves her life by saving her from a dangerous fall. However, to Koyomi's amazement, she weighs next to nothing! Later, Hitagi, who is usually silent, threatens him with a price for his silence. Koyomi, however, refuses to remain impassive and offers his help in solving her riddle.