Kumon Sei is a 16 year old high school boy with an infamous family. His parents, including his father who was a well-known UFO researcher, disappeared years ago without a trace, followed by his two older brothers. Left alone with his father's haunting words, Sei detachedly wonders when he too will be spirited away.
One day, Sei notices a new door in his closet. Curious, he opens it up and finds himself in an unfamiliar apartment. The resident, Oribe Hiroshi, seems unsurprised at his appearance and coolly welcomes him like nothing is odd about the whole situation. However, Sei soon discovers that he appeared in Tokyo about six years into the future! Stranded with not even a toothbrush, Sei wonders if and should he rely on this stranger's kindness. (Source: shinkeikaku)