Mask (2017)

Both have the same concept, despite queen of the ring changes her appearance only one person can see her as her “beautiful” self which is whoever puts the ring on her, and mask is where she becomes an idol due to the mask she puts on she changes from “fat and ugly” to a beautiful idol which people adore

Both female leads are idols and have a secret identity. In Sabu Doru, the female lead is actually 38 years old. In Mask, the female lead isn't what is considered "pretty" in korean standards.