"Inuyashiki Last Hero" centers on Ichirou Inuyashiki, a 58-year-old man who feels alienated from his family and society due to his age and perceived lack of purpose. One evening, while walking his dog in a park, he encounters an extraterrestrial phenomenon that obliterates his body. He awakens to find himself rebuilt as a mechanical being with advanced technological capabilities, including superhuman strength, flight, and the ability to heal others. Unbeknownst to him, a teenager named Hiro Shishigami experiences the same event and is similarly transformed.

Inuyashiki initially struggles to comprehend his new existence but resolves to use his powers to help others, becoming a symbol of hope and heroism. In contrast, Hiro, disillusioned with humanity and embittered by his troubled past, begins using his abilities to inflict chaos and destruction, viewing life as meaningless. The series explores the stark divergence in their paths as Inuyashiki seeks to protect humanity while Hiro descends into violence, culminating in a confrontation between the two.

The narrative delves into themes of morality, the human condition, and the consequences of power. Inuyashiki’s journey is marked by his unwavering compassion and determination to make a positive impact, even as he grapples with the loneliness of his transformation. Hiro’s descent into villainy is driven by his nihilistic worldview and desire to assert control over a world he perceives as cruel and indifferent. The series balances intense action sequences with introspective moments, examining how individuals respond to extraordinary circumstances and the ethical dilemmas that arise from wielding immense power.