Divine Era, year 298, two years before "Yuuki Yuuna's Chapter", Washio Sumi who was chosen by Shinju-sama, is a hero who protects the world alongside her classmates, Nogi Sonoko and Minowa Gin. 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 WaSuYus haven'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 Aki-sensei appointed Sonoko as the leader...
The WaSuYus now have 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.
The WaSuYus 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 daily 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...
Following their battle against the Vertex, YUuna, Fuu, Itsuki, and Karin are joined by a fully recovered Sonoko as the Hero Club resumes its normal activities. However, Yuuna starts to get a strange feeling that someone is missing from the equation. The next day, upon experiencing more deja vu, both Yuuna and Sonoko come to the realization that someone has altered their memories to make them forget all about Tougou, as if she never existed. Upon recalling their true memories of Tougou, who had been taking up a masked hero persona to make up for her sins, the girls are left with the question of where she has disappeared to.
Yuuna and the Hero Club work very hard.
Something surprising happens to the Hero Club again.
There was something written in a certain diary.
Yuuki Yuuna makes a major life decision.