Sou is an ordinary high school student. His biggest worries are his Astronomy Club's project, the zany antics of his fellow club members, and his childhood friend who's suddenly not her usual cheerful self. But then, things take a strange turn...

The kids yawn through a lecture on quantum theory and Schrödinger's cat. And after classes, the Astronomy Club gets to the bottom of the oddly low-tech school festival project of the Computer Club.

Kaori's poor prognosis of recovery from the accident leaves everyone reeling and desperate to find some way to save her.

Yui succeeds in keeping Kaori away from the accident and disappears, almost as though she never existed, but the other members of the Astronomy Club are left with a nagging feeling that they are missing something.

Unaired thirteenth episode delivered as a bonus Blu-ray disc to customers who pre-order all six Blu-ray volumes.