Millennium Snow focuses on Chiyuki Matsuoka, a high school girl hospitalized with a heart problem. Since birth her heart has been very weak and she was told that she would probably live to be only fifteen. However, one day she meets Tōya Kanō, a vampire, with the opposite problem: Tōya lives for about one thousand years. It's customary for a vampire at his age of eighteen to choose a human partner to be with for 1000 years who in turn would let him drink their blood and share his life span for the millennium.

Early in the series, Chiyuki offers Tōya her blood, so that she would be able to live longer, but Tōya refuses, claiming he dislikes the sight and taste of blood. In the beginning, he even looks down on humans, believing that they are weak creatures who will only die before him and leave him behind, but later on he, with the help of Chiyuki, starts to see the world in a different perspective.

Includes an extra story, A Romance of One Moment.