Koriwasen meant a merchant ship that operated a service from Japan to Korea only for the purpose of trade during the Muromachi period. It was also referred to as Korisen.
Since the first phase wako (Japanese pirates) fiercely raided coasts when the Korean kingdom was founded, the Korean kingdom used the profits made by the trade in suppressing the wako. Such powers as Kyushu tandai (the Military Governor of Kyushu), shugo (provincial governor appointed by the shogun), and kokujin (native chieftains, certain local powers) were authorized to have traffic for both diplomatic and commercial purposes, and the ships which brought those envoys were called Shisosen (envoy sending ship). Japanese citizens were also allowed to visit Korea and trade freely with the Koreans, and the ship dispatched for them were called Koriwasen and the Japanese citizens who visited Korea only for commercial purposes were called Koriwa.
Also the operators of Koriwasen were citizens who usually lived on fishing; therefore, since the operators could not trade in such expensive commodities as pepper, tanboku, and copper, they exchanged salt and fish with rice.
Koriwa were originally wako; therefore, they were cunning fellows to the Korean kingdom such that some of them raided Ming and brought their pillage to Korea to trade with Koreans, or were on board bearing arms and traded in their pillage at strictly guarded places and conducted raids as wako on the poorly guarded places. Although the Korean kingdom restricted the port to Koriwasen to enter the Busan Inlet (釜山浦) and Jepo (薺浦) (Chinkae City, Gyengsangnam-do (South Gyeongsang Province) 慶尚南道鎮海市) in 1400 but it was not completely observed; and the Korean kingdom required Koriwa to bear gyojo (passport) issued by the lord of their residence in 1407. That entry restriction would drive Koriwa into a corner -- In 1427, Saemontaro SODA, who was originally wako and influential figure in Tsushima, made a petition to the Korea kingdom to allow them free trade all over Gyengsangnam-do: In response, the Korea kingdom rejected the petition but added Yeompo, Ulsan-Gwangyeoksi (Ulsan Metropolitan City 蔚山広域市) instead. Thereafter, the Soda clan and the So clan kept presenting petitions to increase the ports to enter, but they were not granted. As the ports were restricted, some Koriwa could not find anyone to deal with and stayed in Korea for a long time, and entered private houses and forced the residents to buy their commodities. The Korea kingdom facilitated Koriwasen to leave the port early by purchasing the goods for which Koriwa could not find anyone to deal with.
It was considered that all Koriwasen made Tsushima their base. Although Koriwasen were dispatched from regions other than Tsushima at the beginning of the Korea kingdom, as the regulation on the traffic progressed and traffic expenses increased such as restriction on the ports for Koriwasen to enter, requirement for Koriwa to bear gyojo, enforcement of bunin system (require all the passenger to bear passage permission issued by the So clan), Koriwasen dispatched from the region other than Tsushima gradually disappeared.
In 1510, when the revolt of the So clan and 恒居倭 (Japanese who had been settled down in Sanpo, Korea) failed in the Sanpo Disturbance, Koriwasen were forbidden by the Articles of Japanese Jinshin yakujo and the Koriwasen disappeared.