Kōjin [alternate name samebito] are aquatic humanoids that closely resemble ningyo. Unlike the merfolk of Western legends, Asian merfolk are monstrous in appearance. Kōjin have black, scaly shark-like bodies, and ugly, human-like facial features and arms.
Kōjin are native to the South China Sea, where they live a life similar to other merfolk. They are well known for their skill at weaving, and they spend much of their lives working on their looms. The sea silk that they weave is of the finest quality and doesn’t get wet even in the water. They are very emotional, and cry frequently. When they cry, pearls (or precious gems, by some accounts) fall from their eyes instead of tears.
The kōjin is better known in the West by the alternate reading of its kanji samebito. This is because of Lafcadio Hearn, who included a story about a samebito in his book of Japanese folk tales, Shadowings
Long ago, a man named Tawaraya Tōtarō lived on the shore of Lake Biwa. One day, he came across a strange looking creature crouching near the base of a bridge. It resembled a man, but its body was inky black, it had the face of a demon and the beard of a dragon, and its eyes were like green emeralds. Although Tōtarō was scared, the green eyes seemed gentle to him, and so he approached the creature. The creature introduced himself as a samebito. He had served as an officer under the Eight Great Dragon Kings in the dragon palace of Ryūgū-jō, but was banished from the palace and exiled from the sea due to a small mistake he had made. Since then, he had been wandering, unable to find food or shelter. He begged Tōtarō for help.
Tōtarō pitied the samebito. He took the samebito back to his home, where he had a small garden with a pond. He told the samebito that he could live there for as long as he wanted, and he could have as much food as he wanted to eat. For six months they lived together, and every day Tōtarō brought the samebito fresh food fit for a sea creature.
During the seventh month, Tōtarō went to a festival at Mii-dera, where a great pilgrimage of women had come. There, he met a woman of extraordinary beauty and refinement, with skin as white as snow, and a voice like a nightingale. Her name was Tamana, and Tōtarō fell in love with her at first sight. Totaro followed Tamana home, and discovered that she lived in the same town in which he had met the samebito. He also learned that she was unmarried, and that her family wanted her to marry a man of rank. They demanded as a betrothal gift a casket of ten thousand jewels from whomever wished to marry Tamana.
Tōtarō fell into despair, knowing that even if there were ten thousand jewels in all of Japan, he would never be able to procure them. Though it seemed impossible that he could ever make Tamana his wife, he could not get her lovely face and sweet voice out of his mind. It haunted him so much that he refused to eat or sleep, and became so ill that he could not even lift his head from his pillow. It seemed that he would die of a broken heart. The samebito, whom Tōtarō had cared for in his time of despair, entered the house to care for Tōtarō in his last days. Tōtarō apologized to the samebito, fearing that after his death, the samebito would lose his home and his means of survival, and would die as well. The samebito was so touched by Tōtarō’s compassion that he began to cry. Great tears of blood spilled from his green eyes and down his black cheeks, but by the time they hit the floor they had hardened into splendid rubies.
At this sight, Tōtarō instantly found new strength, and began to gather the jewels. The samebito, astonished at Tōtarō’s recovery, stopped crying. Of course, the flow of jewels also stopped. Tōtarō begged the samebito to continue crying until he had ten thousand jewels, but the samebito regretfully replied that he could only weep when he felt true grief in his heart. Seeing that Tōtarō’s sickness was cured, the samebito was filled with nothing but relief, and thus could not cry anymore. The samebito suggested that they visit the bridge where they had first met to reminisce, and perhaps he could cry again.
The next day, Tōtarō and the samebito visited the bridge. They ate fish and drank wine, and watched the setting sun. Seeing the sun set over the sparkling sea, and with a little help from the wine, the samebito thought about his former life in the sea and his happy days in the dragon palace. He was overcome with homesickness and began to weep profusely. A great shower of jewels covered the bridge. Tōtarō began gathering them up. When he had collected ten thousand jewels he shouted for joy. At the same moment, a delightful song was heard far away in the sea. Like a cloud, a glorious palace made of coral the color of the setting sun rose out of the water. The samebito leaped with joy. He explained to Tōtarō that the Eight Great Dragon Kings must have granted him amnesty and were calling him back home. He bade his farewell to Tōtarō, thankful for his kindness and their friendship, and then dove into the sea.
Tōtarō never saw the samebito again. He brought the casket of ten thousand jewels to Tamana’s family and presented them as a betrothal gift. Shortly after, Tōtarō and Tamana were married.