Devilman by Go Nagai

A sensitive teenager bonds with an ancient demon and becomes a powerful hybrid tasked with defending humanity from rising demonic forces; though he retains human compassion, the escalating violence and paranoia around him expose how thin the line is between monster and man. His childhood friend, a charismatic and secretive ally, pushes events toward a catastrophic revelation that shatters trust and ignites a brutal war between humans and demons, forcing the hero to confront the meaning of identity and loyalty. The narrative builds to an apocalyptic, emotionally devastating climax that unflinchingly examines hatred, otherness, and the loss of innocence.