Early Taishou Era.

Yuu is born to a mistress of the Todou Family, a prominent family, and is mistreated and treated like a slave from an early age.
In particular, her half-sister Nadeshiko pretends to be friendly with Yuu in front of Shinnosuke, whom she has a crush on, but behind her back, Nadeshiko bullies Yuu to no end.
Yuu had hoped to be free someday, but she was unable to do so because she could not abandon her mother, who was locked up in a dungeon.
One day, her mother dies in an unexplained fire, and Yuu, who went to save her, also disappears.

Seven years later, Yuu, who was thought to have disappeared, grows up beautifully as if she were a different person, changes her name to Haruhi, returns to the Todou family, and begins to take revenge for the death of her murdered mother.