The Yeast.

Eighteen-year-old Da-seul was spending an ordinary life helping her father run a traditional makgeolli (rice wine) brewery. However, because the origin of the 'nuruk' (the yeast) that determines the taste of the makgeolli was unknown, their makgeolli could not be officially distributed, and they ended up secretly selling it only to the local villagers. Her older brother, Da-hyeon, who wanted to modernize the brewery, secretly threw away the old nuruk and replaced it with a commercially available one without telling their father or Da-seul. He thought no one would notice—but from that day on, Da-seul fell ill as if possessed, saying "the nuruk is gone." At first, Da-hyeon found it absurd, but as Da-seul's condition worsened, he began to take it seriously. He eventually discovers traces of the nuruk in an unexpected place, and through a chaotic episode involving homeless people, Da-seul and Da-hyeon come to face a truth they had long turned away from.