Following his parents' tragic deaths, wealthy heir Tatsuya Tsugawa struggles to find his purpose. His life shifts dramatically after meeting Seine Miyazaki, an immortal girl hunting deadly, mind-controlling parasites with the help of a mysterious organism.

Haunted by his father's final words about strength, Tatsuya cannot ignore Seine's dangerous crusade against the creatures of the sea. These parasitic bugs seize human hosts to spread hatred, forcing Seine into a constant, violent cycle of eradication.

To battle these pests, Seine utilizes AiON, a bizarre entity that devours the parasites from within. Despite her warning to stay away, Tatsuya resolves to support her, binding his fate to her supernatural war.

In the AiON manga series, Tatsuya Tsugawa assists Seine Miyazaki, an immortal girl hunting parasitic sea organisms with a dark beast.

AiON, AiON manga, Hekikai no AiON, Yuna Kagesaki, Tatsuya Tsugawa, Seine Miyazaki, AiON beast, creatures of the sea, Fantasy manga, Mystery manga