Duo grew up by a different name. He was born into a seemingly normal family and was originally named Noah Kaitou, he grew up in a small village that grew over time, taking in near dead drifter after near dead drifter. Noah's life was a simple one, he trained with a martial artist that lived in the village during the night while attending school during the day. He was a very smart child and constantly praised by his parents. His life was perfect...until he started hearing voices. He would walk through his house, school, even out in the village, no matter where he was he heard that voice saying the same thing "I'm coming for you Noah...and I'm closer than you know..."
The voice drove Noah crazy, it worried him to the point that his academic life fell apart, his family still loved him and tried to get him help...but they knew in their hearts that his problem was not one that could be cured.
Finally it happened, Noah walked through his house alone while his parents were out at a party and his sister was at a friends house, and the voice came again...louder than every. "Noah...I'm here" Duo fearfully ran through the house knocking over everything in his past...this person was nearby and he couldn't do anything, for he didn't see him. Noah ran into his bedroom and locked the door, hid in a corner and held his head while shaking in fear, but he still felt the presense of the person around him. "WHAT DO YOU WANT FROM ME!!?" Duo rose to his feet and ran to the bathroom attached to his room, he locked the door and ran past the mirror over his sink while heading to the window, that's when he noticed it. When he had moved past the mirror, his reflection stood still. He paused at the window while it was half open, then he turned and walked back to the mirror and stared at the person within.
Noah: ...HA! I get it now...this is a dream
???: Wrong Noah...this your life....MY life
Noah: What....what do you mean...who are you?
???: I'm what you should have been Noah...I am the REAL you, and now you shall take your place beneath the surface, while I take over on the surfce.
Noah backed away from the mirror and prepared to dash to the window, but it was to late he was inside the mirror looking out.
Noah: NOOO LET ME OUT YOU MONSTER!!!
???: Sorry kid, but you're to weak to control things here in this world...have fun being the man in the mirror, God knows I didn't...OH! And I'm not a "Monster" Noah, I'm the real you...call me....Duo
Duo turned towards the window and stopped, he walked back to the mirror and placed his hands on it.
Duo: Almost forgot
While his hands were placed on the mirror he absorbed it into his palms, or rather he replaced his palms with the mirror, two circular mirrors, now embedded into his hands.
Duo: Farewell Noah...farewell