Bozo plant?
Was curious what the plant was that the brother and old man were constantly chewing. I had assumed it was similar to the coco leaves in Peru/Chile/Bolivia.
sharePossibly betel leaf (Piper betle), although betel consumption occurs in Southern Asia (Taiwan, Philippines etc.) rather than in Korea. So more likely a fictional plant.
shareI don't think it's betel leaf since that only grows in the tropics. Plus it was from a bush, not a vine growing on a tree.
I had a version with Vietnamese subtitles and it also doesn't say. It just says that when you chew on that leqaf it makes you a man (probably means it makes you horny)