Ichirou Inuyashiki is an old father worn down by the hardships of life, rendering him helpless and weak. Although he is friendless, unloved by his family, and diagnosed with cancer, he decides to try living his best life and adopts a dog. However, while walking his dog one night, the reality of his hopeless situation settles in and he breaks into sobs in a park. But that sadness is short-lived, as an encounter with an extraterrestrial object leaves him with a healthy yet mechanical body. Unsettled by the foreign body and his inability to cry anymore, Inuyashiki starts to believe he has lost his humanity.

However, one night, he saves a homeless man from death, and the sight of the happy and grateful man moves him to tears—proving to him that he is still a human. From that moment onward, Inuyashiki resolves to put his new power to use for the purpose of saving those in need.

Unfortunately, his joy does not last for long, for he finds that there is a new threat determined to revel in its own newfound power through horrifying means. Thus, Inuyashiki's mission turns from being a small-time neighborhood hero to a guardian against a thriving monster.