The story tells about a 17-year-old girl Suzuya who lives in a farmhouse in Kyushu, Japan, and meets a young man who is on a journey to find a "door". Following the young man's footsteps, Suzuya comes to a ruined area on the mountain, where an ancient door stands quietly, as if it is the only relic left after the collapse. Suzuya seems to be attracted by something and reaches out to the door... Soon after, doors all over Japan begin to open one by one. It is said that the open doors must be closed, otherwise disaster will befall the world from the other side of the door.