Inuyashiki centers on Ichirou Inuyashiki, a 58-year-old family man whose life has been worn down by chronic back pain and by the cold indifference of his wife and children, who barely seem to notice him. The one steady comfort he still finds is Hanako, an abandoned Shiba Inu he adopts and brings home, giving him something gentle to hold onto in an increasingly lonely existence.
After a medical checkup reveals that Ichirou has stomach cancer and only three months left to live, he breaks down in a nearby field while clutching Hanako. There he encounters a mysterious figure, and a blinding blast of light, smoke, and dust leaves him reborn as a mechanized weapon wearing the skin of his former self. Shocked but fundamentally compassionate, Ichirou quickly turns his new power toward saving a life, and that first act of kindness gives him a renewed sense of purpose.
But Ichirou is not the only person changed by the incident. Another transformed being emerges from the same event, and while one chooses kindness, the other begins to direct his power toward violence. As their paths move toward collision, the mystery behind their transformation deepens, shaping Inuyashiki into a bleak sci-fi thriller about humanity, responsibility, and the cost of power.