High school student Keita Ibuki, having lost his mother when he was little, lives by himself in an apartment near the coast. One night while eating at a ramen stand he meets a girl calling herself, “Kuro.” Seeing that Kuro is unable to pay for her noodles, Keita treats the girl to a bowl. Kuro tells a tale about how human beings die if they should meet another that looks just like them.
Keita learns of the “Doppeliner System."