Kirk here. These statistics are from 2016 but I saw a reference to Kumamoto’s dependence on tourists from Korea on TV and I think the numbers were similar:
https://honichi.com/areas/kyushuokinawa/kumamoto/
(I have added English to the graphic from the website.)
According to the following article (in Japanese), over the obon holiday (mid-August), the number of Korean passengers traveling from Pusan to Fukuoka via high-speed ferry was down 70%.
https://www.asahi.com/articles/ASM8M3QY2M8MTIPE00K.html
The friction between the two countries is a serious problem for those in the tourism and hospitality industries.