Love Letter From The Future

Ian Percus, a third-year student from the Academy's swordship department, wakes up one morning to find a flip calendar on his desk and a letter he doesn't remember receiving. The letter contains a cryptic message: "If we don't protect the future, the world will perish."
When he goes to the Academy, he finds out that, unbeknownst to him, a week has passed and that during that time, he defeated a previously undefeated junior.
At first, Ian is skeptical, but as the events described in the letter begin to unfold, he gradually starts to believe what is written.
What on earth happened during the week he has no memory of...?
Will Ian be able to protect the future?