Yuuki Yuuna wa Yuusha de Aru: Washio Sumi no Shou

The story of Nogi Wakaba wa Yuusha de Aru takes place 300 years in the past, in 2018, the first days of the Divine Era. The six main characters form the first ever Hero Team: Nogi Wakaba, Nogi Sonoko's ancestor; Uesato Hinata, Takashima Yuna, Koori Chikage, Doi Tamako and Iyojima Anzu.

The story takes place in the era of the gods, year 300. Yuuna Yuuki lives an ordinary life as a second year middle school student, but she's also a member of the "Hero Club," where club activities involve dealing with a mysterious being called "Vertex."

(Source: Anime News Network)

In the year 298 from the era of the gods, elementary school girls Sumi Washio, Sonoko Nogi, and Gin Minowa are tasked with an important mission. They are to become heroes and fight Vertex, a mysterious enemy that is attacking Shinju-sama, the god tree that protects Shikoku, the only area in the world that is still habitable. What they don't know, is that this fight will cost them more than they could have ever imagined.

In the year 298 from the era of the gods, elementary school girls Sumi Washio, Sonoko Nogi, and Gin Minowa are tasked with an important mission. They are to become heroes and fight Vertex, a mysterious enemy that is attacking Shinju-sama, the god tree that protects Shikoku, the only area in the world that is still habitable. What they don't know, is that this fight will cost them more than they could have ever imagined.

Note: The first of two manga adaptations, as this serialization was eventually cancelled.