So, there's this super-exclusive prep school, and everyone who graduated from it becomes the elite of the country. There's no traditional entrance exam, though. Instead, there this mysterious floating island that appeared above the city, and not everyone can see it, and the only people who are admitted to the school are people who can see the island.
The very first thing they ask the students on their first day of class is "what do you need to survive? write down the kanji that best exemplifies what you think you need." (That's where the title comes from) So the hero writes "change" because he wishes he could change into a better person. The heroine is the heir to a prestigious sword-fighting style, so she writes "sword."
Suddenl, when the shadow of the floating island passes over the school, monsters attack. The teachers won't help, they leave the students to fight the monsters on their own.
Turns out, whatever kanji you wrote becomes your power. So the sword girl can manifest a katana to fight the monsters with. And the guy who wrote "change?" Well, he really does turn into an entirely different person.
