Leviathan is a dark sci-fi horror manga set in a post-apocalyptic underwater world, following the survivors of humanity who live in deep-sea colonies as they face monstrous creatures and the psychological toll of living in the crushing depths. As they struggle to survive against the terrifying leviathans that roam the ocean while dealing with the claustrophobia and isolation of underwater existence, the narrative explores themes of survival, fear, and the fragility of human civilization with atmospheric horror and stunning underwater visuals. Blending sci-fi, horror, post-apocalyptic, and psychological elements with deep-sea setting, the series delivers chilling storytelling that appeals to fans of underwater horror and dystopian sci-fi. Also known as Leviathan manga, リヴァイアサン, deep-sea horror, post-apocalyptic sci-fi, and seinen horror.