An unfortunate title because while it's technically accurate -- that's not something the narrator is bragging about.
A class of students from Japan are summoned magically into a fantasy world and told they have magical powers now, though only one of them will be the Hero, and are needed to help. Akira, the main narrator, at first thinks it's everything he loves in a story, and that being an Assassin is cool, but when he realizes that his powers are vastly larger than others' -- even the Hero's -- he's unnerved and hides his abilities. That night he uses them to sneak about and hears the king and princess discussing how the summoned people do not realize what they are up to.
The story involves a very RPG