Hiiro Okamura, a book-loving loner, is swept into a summoning meant to bring four heroes against the demon king of the Evila, and arrives as an unwanted fifth. Seeing through the kingdom's motives, he refuses the role and walks out to register with the Adventurers Guild on his own terms. His one advantage is the title Word Master: writing a character makes its meaning real, so a single stroke can become fire, a wall, or speed. Hiiro crosses the world as a free agent while the four chosen heroes carry the war.