Passage: The ruler of Qin Dynasty, Qin Shi Huang, feared death and sought a way to live forever. He entrusted Xu Fu with the task of finding the secret elixir of immortality. In 219 BC, Xu Fu was sent with three thousand virgin boys and girls to retrieve the elixir of life from the immortals on the Mount Penglai, including Anqi Sheng, who was purportedly a magician who was already a thousand years old. Xu sailed for several years without finding the mountain. In 210 BC, when Qin Shi Huang questioned him, Xu Fu claimed there was a giant sea creature blocking the path, and asked for archers to kill the creature. Qin Shi Huang agreed, and sent archers to kill a giant fish. Xu then set sail again, but he never returned from this trip. The Records of the Grand Historian says he came to a place with "flat plains and wide swamps" (平原廣澤) and proclaimed himself king, never to return.

Question: Who set sail but never returned after Qin Shi Huang agreed to help by sending archers to kill a giant sea creature?
Xu