The main character is living the normal life of a High School student.

Right before Summer Vacation he makes up his mind to ask out beautiful Kaho Serizawa, but the very next day he wakes up to realize that Summer Vacation is over and he has "Day Dropped", or time-slipped, to September 1st.

Going to school in a state of confusion, the main character finds his grief-stricken classmates, who tell him that his girlfriend Kaho has died in a tragic accident on August 31st. How did he start dating Kaho, when he doesn't remember asking her out? And what were the tragic events that lead up to her death?

Day dropping back and forth into time, the main character grapples with the problem of how to overcome this terrible fate awaiting the girl of his dreams.

A summer vacation that crosses the boundaries of space and time.