From Tokyopop:

Yuuki is an energetic teenager who carries the disturbing power of foresight in her dreams. She finds that this is tied to the mysterious Deep Sleep that has overtaken her sister, Yuuka.
Clues left on her cell phone and visions that come to her in her dreams begin to reveal a strange puzzle... and then in one dream, a glass wall stands between her and her sister while a faceless little girl stands by Yuuka. The mysterious girl hands Yuuki a kaleidoscope--which Yuuki discovers she still has when she awakens from the dream the next morning...