A group of second-year high school students from Yoshinomiya Municipal High School set out on what is meant to be an educational cruise, a chance to enjoy time with friends away from their families. However, their journey is violently interrupted when their ship is caught in a sudden, fierce storm, causing it to crash and sink near an uncharted island. The surviving students wash ashore on this mysterious landmass, only to quickly realize they are not alone. The island is home to a primitive and hostile tribe known as the Shimabito or the people of Ingoshima. Far from being rescuers, the islanders immediately begin hunting and capturing the stranded teenagers. The students find themselves trapped in a savage society where violence, sexual abuse, and human sacrifice are a routine part of life, and where their modern morals and ethics are put to the ultimate test.

The central protagonist is Keita Todoh, a pragmatic young man driven by his determination to protect his childhood friend, Aoi Miyahara. Aoi is a beautiful and resilient girl with long black hair who unfortunately becomes a primary target of the islanders. She is quickly captured and designated to become the wife of Gamou, the island's brutal and powerful king. Keita manages to avoid the initial capture and joins with other survivors, including Shinnosuke Tachibana, a skilled kendo practitioner with a cool and collected demeanor, and a handful of others, to fight back. Their primary goal quickly becomes a two-fold mission: rescue their captured classmates and find any possible way to escape from the island.

The initial narrative arc focuses on the immediate aftermath of the shipwreck. The students are hunted down one by one, with many being killed and the majority, especially the girls, being taken as sex slaves. Aoi is singled out by Gamou, who becomes obsessed with her due to her resemblance to his long-lost first wife. Another key arc follows Keita as he and a small resistance group, including Shinnosuke, attempt to infiltrate the main village to steal a boat's fuel and free their friends. This mission is fraught with danger, leading to brutal confrontations with the island's warriors, such as the master swordswoman Jiubee. The story also follows the fates of the captured students, like Kana Sasaki, who face sexual slavery, and Aoi, who, while slated to be queen, must resist Gamou's advances and maintain her sanity and will to survive.

The island of Ingoshima is a tribal society structured like an ancient kingdom. The strongest warrior, Gamou, rules as king, advised by his mother, Chiomo, who also serves as the high priestess. The society is deeply patriarchal, with men as the ruling class and most women living in subjugation as laborers or for reproduction. The islanders speak a strange dialect of Japanese and are fiercely xenophobic, viewing outsiders with extreme hatred. They believe themselves to be the children of Ingoshima, a clan abandoned by the mainland long ago. Their cruelty is ritualized in ceremonies like the Omegumi, where captured outsiders are drugged and questioned; those who forget their names are either fed to sharks or thrown into a volcano. A mysterious element of the setting is that the island is surrounded by perpetual storms and a strange magnetic field that paralyzes communication devices and prevents ships from finding it or leaving, ensuring its isolation and the cycle of shipwrecks that replenishes its population with fresh victims.