After a monologue about loneliness and a famous quote from Edgar Allan Poe, an unknown mysterious narrator tells the protagonist that nothing is real
and urges him to jump. When he decides to do so, the mysterious protagonist is awakened in a classroom,
by an unknown redhead teenage girl with pigtails.
The protagonist is not able to recognize the place he's in or the girl in front of him.
Not recalling his first or last name either, he decides to stick with what the redhead seems to call him: Sensei. The classroom he finds himself in has a sense of familiarity but he still cannot remember anything. The girl grows progressively worried as he is not able to remember her name either or the fact that the two of them live together. She then reveals herself to be Ami Arakawa, his student and niece.
As Ami decides to guide him back home, it becomes clear how some of Sensei's thoughts seems rather dark.