Made in Abyss: Made from Fortunes

Fyuo, a shy and cowardly red whistle, finds himself plagued with nightmares of a beast. His best friend Kwazan, feeling like there is more to the story, drags him into an adventure to find it, only to find themselves set up for a much deeper rabbit hole after meeting the protagonist of Fyou's nightmares. What secrets await them not only below in the depths, but up to their roots back home?