Shizun and Bom are a couple who lives in Seoul, they are a couple since first year of high school. Bom and Shizun are both asian, Park Bom is a Korean guy and Shizun Made is a Japanese guy.
In South Korea, there is a tradition that a first boy born child can't marry foreigners because they want to follow their tradition and if they broke or unfollow it, it's a big insult in their culture. They can only marry someone with the same nationality like korean.