Moss on the wall

Moss friends living a peaceful daily life in a terrarium do their usual work of washing away carbon dioxide and purifying it with oxygen. But one day, while washing Soot from fine dust, Soot runs away, and while trying to protect Soot from a fatal attack from the Ultraviolet Demon King, Seori's mother is poisoned instead of Seori. After hearing from her knowledgeable grandfather, Moss, that the Moon Lotus Seeds can cure her mother, whose life is in danger, Seori decides to travel outside the terrarium.