'Fill in the Blank' is based on the hypothetical psychological theory that the highly materialized life of modern people can be explained with 9 objects in any case. It is a documentary that contains the journey of four K-Pop idols - Oh My Girl's Hyojung, The Boyz's Q, ATEEZ's Wooyoung, and LESSERAFIM's Kim Chaewon - to find nine objects that express and explain themselves.