Yato is a 22-year old; a normal fourth-year in university troubled with money.

One night as he leaves later than usual from campus, Yato finds a strange object on the ground-- a black card with just the single number [9] written in reverse. When he inserts it into an ATM, Yato realizes to his surprise that the black card functions as a cash card, holding a sum beyond his wildest imagination----Displayed on the screen is a string of 9s---- [$999,999,999,999]!

What secrets lie within the origin of this black card? Inevitably tumbling into the webs of a yet unseen world, Yato is probably the only one to find out. With a facade that hides his emotions, Yato clutches the black card tightly in hand and takes his first step on this treacherous path.