After having spent most of your life living aimlessly, you even contracted cancer and were on the verge of death.
Something happened to you during your high school days, and you have always felt regret over what happened.
During your school years, a crazed serial killer entered your school and murdered every last student.
The girl that you had liked at the time was also killed right in front of you. You regret that you had frozen from fear and not tried to save her.
Suddenly, a mysterious person appears in front of you as you lie on your deathbed.
He says, “I will allow for you to relive your school days. BUT, you must not let anyone find out that you are from the future. If someone finds out that you are from the future or if you cannot save the person that you loved, not only will you die, but you will also suffer through an eternity in hell.”
Instead of just dying of cancer, you decide that you would like to have a chance to save your past love. Therefore, you decide to relive your high school days.
When you wake up, you are in your teenage body once more.
The girl you saw die is stands right in front of you...alive...