7화: 영어 교사 사이노 히이라기는 고인의 교수로부터 파이 책을 받아 과거로 돌아가 어린 시절의 자신에게 건넨다.

7

Saeno Hīragi, an English teacher, receives a book containing part of the value of pi from her deceased mathematics professor. After returning to the university at which he had taught, she goes backward in time and gives the book to herself as a child. (Source: Wikipedia)