Since When Does Light Yagami Have a Twin Sister?!

The screech of tires and the crunch of steel were the last things she knew. When she opened her eyes again, she was given a new name: Yagami Tsukiko.
She spent three years desperately clinging to the idea of coincidence. Sure, her surname was Yagami, and yes, she had a brother named Light who was far too intelligent for a toddler-but she refused to believe she had been reborn into a world of Shinigami.
That denial shattered the moment her father brought a new bundle of blankets home from the hospital.
"Meet your sister," Soichiro beamed. "Sayu."
As she stared at the infant, the cold truth sank in. This wasn't a fluke; it was a script. And if the story followed the one she remembered, her "perfect" twin brother was destined to become the world's most wanted god.

But wait minute...if this is Death Note... SINCE WHEN DOES LIGHT YAGAMI HAVE TWIN SISTER?!