both have revenge plot which makes it kind of similar. in glass mask the FML is tourtured for the reason that her father was a criminal so she assumes another woman identity to take revenge

they both have dark concept around a school theme which makes both of them similar. in extracurricular ,Determined to escape a dead-end life, a gifted high school student turns to a life of crime to ensure he can pay for college. I basically liked this drama and so I wanted to see Shadow Beauty.

Both are revenge kdramas. The series follows Kang Yi-kyung, a woman whose father is a murderer. She must deal with tough times i.e. her boyfriend leaving her, her family which adopted her also left her and she was harshly treated because she was a murderer's daughter so she plots her revenge. To fulfill her revenge, she assumes another woman identity and comeback as Seo Jung-ha.