Penglai Island is one of the three legendary fairy islands. Daishan was called Penglai Fairy Island in ancient times. Daishan County is located in the middle of Zhoushan Islands along the northern coast of Zhejiang, at the southern end of the Yangtze River and Qiantang River estuaries, on the outer edge of Hangzhou Bay, on the back Close to the large and medium-sized cities of Shanghai, Hangzhou and Ningbo, it is between 30.7'-30.38' north latitude and 121.31'-123.17' east longitude. It connects to the high sea in the east; to the Huang Dayang in the southeast, connecting the waters of Putuo District, Zhoushan City; to the southwest to the Gray Turtle Ocean; to the south to Guanmen Waterway, intersecting with the waters of Dinghai District; to the west, it reaches Qibi Bamei Island in the Gray Turtle Ocean, which is connected with Pinghu City It borders the waters of Cixi City and Chuanhu Islands in the north, and is adjacent to the waters of Shengsi County.

Legend has it that there is an island in the sea where humans and monsters can live in peace and harmony. It is called Horai Island and is guarded by the powerful shrine maiden Zuo Ji. Because it is common for humans and monsters to intermarry, many half-youkai are born on the natural island. However, the hostility of the outside humans and monsters towards half-youkai makes them reluctant to let their children leave the island, so Suuji protects the island with a barrier so that outsiders cannot see it. It is also not allowed to enter. There is a huge "sounding furnace" on the island's volcano, which is the power source of the entire island's barrier. And every fifty years, the power of the barrier will weaken. At this time, foreign monsters often invade the island and want to seize the spiritual power in the furnace. Finally, Penglai Island was conquered by four powerful monsters who called themselves the Four Gods of Fighting. Suuji was defeated, lost most of her spiritual power, and her soul turned into a firefly and was sealed in the furnace. However, she managed to capture the souls of the Four Fighters and hide them within a very strong barrier. Therefore, the Four Fighters were turned into living corpses. Not only did they lose part of their power, they also had to absorb the spiritual power of others regularly, otherwise they would gradually weaken and turn into phantoms. So they left the residents of the island as food. Among them, the half-demon had both human spiritual power and monster power, and became the main food of the Four Fighters. The residents who were sucked dry turned into fireflies and spread everywhere. After being marked, almost all the half-demon on the island (the children at the beginning) could not leave the island. Only the youngest Lan was not marked, so he escaped from the island and met Inuyasha and his party. Of course, because he is a half-demon, he grows slowly. Lan met Inuyasha once fifty years ago. At that time, Naraku had not yet attacked Kikyo. Inu and Kikyo happened to encounter the appearance of Panglai Island when they were boating on the beach. During the brawl, Inuyasha was also marked by the boss of the Four Fighters, and Kikyo was sucked by the fourth. Moreover, the second of the Four Gods of Fighting killed two monsters under General Inu and took away their weapons. Sesshomaru was too late to save him, and he was also plotted to be marked by the second. So both brothers have some old grudges with the Four Fighters. Therefore, the reappearance of the island is also a good opportunity for them to eliminate the marks on themselves.