Yuuki Yuuna is a Hero: Washio Sumi's Chapter 3 - Promise

Jr. High School Student Wataru and his friends like playing in an abandond building and looking for ghosts. However it seems he is not the only one. Another mysterious student Mitsuru shows Wataru that there is a magical door to another world where one can go and get the Goddess of Fortune to grant one wish! When tragedy strikes Wataru's family he decides to open the door for himself.

The battle is over, and they can go about their normal lives now... or so they thought. With no time to rejoice after miraculously saving Mirai from Beyond the Boundary, Mirai lost all her memories. Akihito, now a high school senior, starts to avoid Mirai thinking it’s for the better. Not aware of Akihito’s feelings, Mirai tries to get closer to Akihito. Then, someone who knows of Mirai appears in front of the two. With Akihito’s troubles in vain, Mirai once again sets forth on a battle that forces her to look within.

While struggling to make friends after his parents’ divorce, Koyomi Takasaki meets Kazune Takigawa, but apparently, they already have. Kazune reveals that she’s from World Line 85, an alternate universe in which she and Koyomi are lovers. But in a reality where moving between dimensions is natural, could Koyomi be the one from another world?

A fourth-grader investigates the mysterious reason behind the sudden appearance of penguins in his village, which is somehow related to a power from a young woman working at a dental clinic.

Arata inadvertently touches "Hermes Apocrypha," Lilith's Grimoire. Suddenly, he is enveloped by a bright white light, and a girl appears before him. She calls herself Lilim, and treats both Arata and Lilith as her parents. At the same time she appears, something changes in the world. The forbidden Eternal Library awakens.