Two years before "Yuki Yuna is a Hero." Sumi Washio is only in 6th grade, but she's a hero who was chosen by Shinjyu to save the world. Sumi fulfills her role while cherishing her precious regular life with her classmates, Sonoko Nogi and Gin Minowa. The story moves onto Yuki Yuna from Sumi Washio. An incident occurs at the Sanshu Middle School Hero Club who used to have a peaceful everyday life.
Era of the Gods, year 298, two years before "Yuki Yuna is a Hero." Sumi Washio(6th grade) who was chosen by the Shinjyu, is a hero who protects the world alongside her classmates, Sonoko Nogi and Gin Minowa. It seems like Sonoko and Gin are trouble-makers because they could be idiotic or too energetic. Sumi is excited that she should lead the other two, but...
The hero team, Sumi Washio, Sonoko Nogi, and Gin Minowa, hasn't been able to unify because they haven’t had much time to prepare. So, they decided to choose a leader and strengthen their unity by doing a training camp. Sumi saw herself as the leader, but the teacher, Ms. Aki appointed Sonoko as the leader...
The three girls, Sumi Washio, Sonoko Nogi, and Gin Minowa, who now has stronger unity, are working hard to fulfill their roles as heroes. It’s part of their job to rest as well. Three of them started to fully enjoy their momentary break.
Sumi Washio, Sonoko Nogi, and Gin Minowa are going to their elementary school's class trip. The three of them are put in a crisis because of the Vertex's advanced action whom appeared as if to shatter their fun everyday life.
The Hero's system advances to prepare for the battle with the escalating enemy. However, that was too brutal for the girls in 6th grade to have to bear. Nevertheless, the girls work hard to fulfill their roles.
Finally, the climactic battle has begun. The heroes are fulfilling their roles with full of new powers. The flowers bloomed beautifully. What kind of destiny would await them in the future...
Mimori Togo looks back on the days since she entered the Sanshu Middle School, the day she became a hero and faced the Vertex with her friends, and the day she was troubled by the risk of the “All out.” That's a memory of a pure and fleeting flower.
Yuna Yuki and the others at the Sanshu Middle School Hero Club work hard at their club activities, and spend their everyday life as usual.
Yuna and the Hero Club work very hard.
Something surprising happens to the Hero Club again.
There was something written in a certain diary.
Yuna Yuki makes a major life decision.
Heroes' screams echoed out into the heavens.