In the deep ocean, mermaid Jo lives peacefully until her friend Ryuu is jailed for exposing their hidden undersea world to humans. Jo embarks on a quest to save Ryuu, unraveling secrets that could involve love.

Humanity knows little of the deep ocean, where a hidden mermaid nation thrives thousands of meters below. Here, the mermaid Jo enjoys a quiet life until a grave violation shatters her peace: her friend Ryuu is imprisoned for exposing their world to humans.

Jo must uncover why Ryuu betrayed their sacred law and who she told. This dramatic fantasy romance follows Jo's adventure to free her friend and confront burgeoning feelings.

A Sinner of the Deep Sea manga: Mermaid Jo's peaceful undersea life shatters when friend Ryuu is jailed for revealing their world to humans. Jo fights to save her.

A Sinner of the Deep Sea, Jo, Ryuu, Mermaid, Undersea World, Fantasy, Drama, Romance, Read Manga, Completed Manga