My Status as an Assassin Obviously Exceeds the Hero's (Light Novel)

Akira Oda is a high school student who has the special "skill" of not being noticed. He, along with his classmates, are summoned to a fantasy world of sword and sorcery where they are powerful heroes tasked with defeating a dark lord by a king. With his newfound skills as an assassin, Akira soon uncovers a plot by the kingdom's royal family, and is cast into a labyrinth to die. He swears vengeance on the king, and seeks more power to achieve his task.