After her werewolf lover unexpectedly dies in an accident, a woman must find a way to raise the son and daughter that she had with him. However, their inheritance of their father's traits prove to be a challenge for her.
Kyuta, a boy living in Shibuya, and Kumatetsu, a lonesome beast from Jutengai, an imaginary world. One day, Kyuta forays into the imaginary world and, as he's looking for his way back, meets Kumatetsu who becomes his spirit guide. That encounter leads them to many adventures.
Unhappy after his new baby sister displaces him, four-year-old Kun begins meeting people and pets from his family's history in their unique house in order to help him become the big brother he was meant to be.
