No Korean visa is required. According to international travel regulations, if you depart from Shanghai, transfer in Incheon to Japan, do not check in luggage, and hold a non-connecting ticket, normally you do not need to apply for a Korean visa. During the transfer process, you may need to go through certain immigration procedures at the Korean airport, but you do not need to apply for a visa in advance. However, the specific situation may vary due to changes in visa policies. It is recommended that you check the latest visa information before traveling.