densetsu no yuusha no densetsu
伝説の勇者の伝説, "The Legend of the Legendary Heroes"
A light novel series written by Kagami Takaya and illustrated by Toyota Saori. Also adapted into a manga with art by Toyota, Chouzo Hiroko, S. Kosugi, and Hozumi Riya. An anime adaptation by Zexcs aired in 2010.