Karappo no Shoujo to Niji no Kakera  

A Girl With an Empty Heart and Fragments of a Rainbow, 空っぽの少女と虹のかけら

In this story, we meet Poyoko, who felt like nobody wanted her. She then heard a strange voice that led her to a new world filled with unusual creatures. While exploring this new place, she came across a boy with a unique mask. This marked the beginning of their dark fairy tale as they embarked on a quest to find the pieces of a rainbow.