The novel ran concurrent to the original anime. It goes into depth on things that are discussed in the later half of the series. The novels later received a Comic-Book Adaptation in 2014 as well as an Animated Adaptation in the form of Washio Sumi Chapter. The anime was originally aired as three films before airing on television as the six episodes of Yuki Yuna Is A Hero's second season.
Washio Sumi is a Hero provides examples of:
- Adaptation Expansion: The Washio Sumi Chapter movie trilogy expands the plot of the original novel it was based on by adding more scenes relevant to the story and to the main trio's relationship as well as by giving their once unnamed teacher a name that possibly connects her to one of the characters from the Nogi Wakaba novels in the adaptation.
- Asleep in Class: Sonoko falls asleep in class a lot. Her introduction scene involves her awaking during class.
- Bittersweet Ending: The series ends on a bittersweet note, with an emphasis on "bitter". Gin is dead, Washio is amnesiac and paralyzed, and Sonoko is forced out of elementary school and bedbound with several physical impairments. However, it does end with Yuna meeting Togo.
- Call-Forward: The anime contains several to Yuki Yuna is a Hero:
- Sonoko tells Washio that she should learn to pull pigeons out of her hat. Togo was shown doing this with doves.
- Washio mentions "alpha waves" while moving her hand, just like Togo did.
- The scene where Washio realizes she can't move her legs mirrors the scene where Yuna realizes the same thing.
- At the end, Sonoko leaving Washio to fight parallels when Yuna did the same thing to her.
- Sonoko gives Washio a ribbon which she wears even as Togo, despite not understanding why.
- Child Soldiers: Gin, Sonoko, and Washio are eleven year olds who are chosen to fight for the world's safety. Their lives are on the line each time they fight.
- Establishing Character Moment:
- Washio's intro, including helping make her family breakfast, shows that she's a responsible and rich girl with some traditionalist views.
- Sonoko falls asleep in class and wakes up abruptly, showing that she's laidback.
- Gin rushes to class after the teacher already arrives, foreshadowing that she's reckless and Hot-Blooded.
- Evolving Credits: The outros change throughout the episodes.
- Foregone Conclusion: Washio Sumi Chapter came out three years after the original anime ended. Fans who watched it know that Sonoko will end up bed-bound and Washio will both lose her memories and end up in a wheelchair.
- Freeze-Frame Bonus: In the second episode, Washio's internet history consists of searches on how to make friends in elementary and on the history of Japanese navel ships.
- Kid Hero: The three girls are all eleven year olds Magical Girl Warriors who protect their island. However, they're closer to being Child Soldiers considering what being a Hero entails.
- Magical Girl Genre Deconstruction: The characters are elementary schoolers who fit the requirements to become Heroes. However, being a Hero isn't as pleasant as it initially seems. By the end of the series Gin is dead and her two friends are traumatized.
- Magical Girl Warrior: Magical Girls are called "Heroes" and they work together in teams.
- Ms. Fanservice: Washio gets the most fanservicey Transformation Sequence.
- Named by the Adaptation: Aki-sensei was originally only referred to as the girls' teacher in the original light novel.
- Patriotic Fervor: Washio is obsessed with Japanese history, Japan's military achievements, and staying traditionally Japanese. She even wants to be a historian some day. Her comedically patriotic nature is Played for Laughs.
- Ship Tease: It's implied that Washio likes both Sonoko and Gin (especially Sonoko), but her friends feelings are more vague.
