Shiryoku kensa manga

Shiryoku Kensa summary:

From Chinatown KM: Miyashita Megumi, also known as "Gumi", was one of the only survivors in a plane crash thirteen years ago. Since then, she has been able to see two copies of every person and one of them always has a "C" on them. Thirteen years later, she now wears glasses, yet her left eye remains a puzzle. And then, her friend goes "missing".