Kusunoki Mebuki was up to compete for the hero's position, but lost to Miyoshi Karin. This left a jealous stain on the girl. She was later summoned to Kagawa's Gold Tower, where she was given a new duty as a sentinel, a soldier whose job is to stand by and keep watch. Now along with three other sentinels and a priestess, Mebuki will fight and protect her army, the current generation of heroes, and the rest of humanity from the creatures who hide behind the wall.

(Source: Yuki Yuna is a Hero Wikia)