Picture book author Hotaru Yuuyami lost his beloved dog, Hanako. He was in the depths of a dark and deep sadness, regretting his inability to do anything about it. One day, he notices a pink mushroom growing under the snow willow tree in his garden. As he gazed at it idly, it suddenly began to move, wagging its tail and coming closer to him. “A mushroom...dog?” 

Despite his doubts, he decides to live with this mysterious creature, “Kinokoinu" (Mushroom Dog). Then he started drawing where he wasn't supposed to draw, ate all the melon bread and takoyaki, and made all sorts of messes, but his playful attitude is hard to hate. 

The days spent with Kinokoinu, involving his childhood friend Komako-chan, the editor, and Yara-kun of the Mushroom Research Institute, gradually changes Hotaru's expression. This is a slightly mysterious and heartwarming animation that depicts the funny days of Hotaru and everyone together with Kinokoinu, who is too mysterious in many ways. 
(Source: Crunchyroll News, edited)

The heartwarming story centers on a Mushroom Pup who is one day born in the yard of picture book author Hotaru Yūyami. It wags its tail just like a dog, but it's unknown if it's a dog or a mushroom. It draws pictures where it shouldn't, and always wants to eat Hotaru's takoyaki. 

(Source: Anime News Network) 

Note: Includes 8 extra chapters.