Remember 11: The Age of Infinity

Snowy Mountain Arc
Fuyukawa Kokoro, a third-year sociology major, boards a plane for Hokkaido to meet a study subject in the Specified Psychiatric Hospital for Isolation and Aegis, or SPHIA. For unknown reasons, her plane crashes into a mountain in the middle of a snowstorm. Out of the 31 passengers, only she, Yuni Kusuda, Seiji Yomogi, and Lin Mayuzumi are able to survive unharmed. Unable to establish communication with the outside world due to the fierce snowstorm, the four decide to take shelter in an abandoned cottage and wait until the storm passes.
As if the trauma, freezing temperature and hunger weren’t enough to endure, the survivors must deal with something even more frustrating. A newspaper is found in the cottage dated July 4, 2011 (which is the future to the survivors). The paper claims that the remaining survivors of the crash, except for Yuni, will die in an avalanche in seven days.

SPHIA Arc
Satoru Yukidoh, a graduate student in the field of quantum physics, falls off of the SPHIA clock tower for an unknown reason. He later awakens with some memory loss and the realization that someone is out to kill him. Unable to leave the SPHIA facility due to a snowstorm, Satoru’s only chance at living is to find that person among the three other residents (or perhaps the hidden culprit) of SPHIA.
Both Kokoro and Satoru soon realize that, their “consciousness” experience a kind of exchange which allows Kokoro’s mind takes control of Satoru’s body in SPHIA and Satoru’s mind takes control of Cocoro’s body in the cottage/emergency shelter in the mountains.
However, a boy named Yuni Kusuda appears at both locations. How is this possible?