Oh Sehun entitles Song Ahri as a mysterious girl. She's that quiet pretty girl who always sits at the corner of the room. Someone who isolates herself away from people. She isn't the nosy brat, nor the geeky type, nor the queenka type, perhaps just the loner type. It had piqued Oh Sehun's interest. For a year and a half, he stood behind the shadows, satisfied just by observing her from afar, but no, not this time. He is determined to unravel her little secrets, how does he know that she has secrets?

               He just can feel it.

               Why does he even care?

               He's simply bored.

    Song Ahri noticed Oh Sehun lurking behind the shadows. Somehow, things bends and straightens, little mysteries starts unraveling, those tangled threads untangles, and somehow Oh Sehun and Song Ahri, plays a little game called the 'Fifth Secret'.

 Whereas the game ends when Oh Sehun finds out the Fifth Secret.