Hanakisou

From Storm in Heaven:

The Prophet spoke of a day when the taking of human lives will lead to the end of the world, destroyed by an unending winter and a snow that covers the earth. Only by killing Kuroto, the harbinger of destruction, can the world be saved - and the only one who can do that is Hanashiro, the Savior. But when they meet, they discover that neither wants the role he has been given - and as they grow closer, they realize that neither wants to live in a world where only one of them can survive. But how can they overcome this fateful prophecy and their opposing roles in it? The last winter is fast approaching....