Minsoo and Yoonji's world exists within an enclosed dome devoid of nature - not that they remember what "nature" is, of course. A myth goes that there's something called the sunrise - golden orange, bright and warm. It's somewhere "outside there" but nobody knows where, and if it even exists. Yoonji is a chaser of the sunrise and Minsoo is a skeptic, until he himself sees the rumoured sunrise in his dreams.
1 part