A twin, to be exact. The only difference between him and Rumer was that she was a girl. People would stare at the two of them, whisper to themselves about how uncannily alike the two of them were. But they didn't care. They were each other's best- and only- friend. Their hearts beat as one, and so they fancied themselves- one person in two bodies. And when their powers appeared, they could easily have four bodies, or seven, or ten. It didn't matter what they did; so long as they were together, they were content. They had been born together, and they would grow old and die with none but each other. They knew this in their hearts.
Until the day Rori woke up, and Rumer wasn't there beside him. He panicked, searching for his sister through the special bond that all twins shared, but it was as if she had disappeared into thin air. Their parents had dumped the two of them off at the nearest orphanage when they were two, she was the only thing that mattered to him in the world. It was as if his sun had vanished, and alone and freezing, he had been left to wander. The orphanage director alerted the police, but all evidence pointed to Rumer having run away- though her stuff was untouched, all of her files were missing. The officer assigned to her case even went so far as to say that, according to birth certificates, Rumer Tertly had never existed.
But Rori knew that wasn't true. He could feel the shadow of her inside of him, knew she was out there somewhere. He tried to create an army of dopplegangers to help his search, but his power hadn't worked since Rumer had gone. They needed each other, they could hardly function apart.
Rori is still looking, though it's been almost a year. His eyes are bloodshot, and he swares he hasn't slept since she left. Occasionally, he thinks he hears her calling, or glimpses her out of the corner of his eye. People say it's all in his head, but he knows she's out there, because the shadow of her within him talks to him in the dead of night, whispering the secrets only his sister could know. He couldn't have just created a sister out of thin air, anyway.
That would be uncanny.