Fun fact: even today, kimchi (and food in general) in North Korea is less spicy than the South, because they've basically missed out on 50 years of culinary evolution.

https://www.youngpioneertours.com/north-south-korean-kimchi/

Likewise, while Japanese cuisine is generally not spicy at all, the few outliers like mentaiko generally originate from the southern regions like Kyushu and Okinawa that traded with Korea & China.