In fiction and folklore, a doppelgänger ordoppelga(e)nger (/ˈdɒpᵊlˌɡɛŋə/ or /-ˌɡæŋə/;German: [ˈdɔpəlˌɡɛŋɐ], literally "double-goer") is a look-alike or double of a living person, sometimes portrayed as a paranormal phenomenon, and is usually seen as a harbinger of bad luck. In other traditions and stories, they recognize one's 'double-goer' as an evil twin. Doppelgaenger is a german word which also means double walker.

In Woohyun's case, his doppelgänger appeared as a messenger to tell about a future dreadful event that going to happen to his best friend, Sunggyu.

Will Woohyun being able to save Sunggyu?

Or will regrets going to haunt him for his whole lifetime?