Harry Potter
Harry Potter is easily one of the most successful franchises of all time. In a twist that spanned the duration of the series, it turned out that Snape was a good guy all along. The Potions Master and Head of Slytherin House secretly shielded Harry from evil during his time at Hogwarts because he was madly in love with Harry's deceased mother, Lily.
A Tale of Two Sisters
In A Tale of Two Sisters, Su-mi (Yeom-Jeong-ah) watches over her timid younger sibling Su-yeon (Su-jeong Lim); both sisters hate their evil stepmother Eun-joo (Kap-su Kim), who once served as their late mother's nurse. It is revealed that Su-mi suffers from dissociative identity disorder, acting as both Su-yeon and Eun-joo after experiencing the traumatic loss of her sister, who was crushed by a wardrobe with her mother's dead body hanging inside. However, we later learn that Su-yeon actually is a ghost, who traps and kills the real Eun-joo offscreen.