After Kidnapping the Villain's Daughter, She Hired Me to Overthrow the Wealthy Family.

In order to raise money to save his sister's life, a low-level gangster kidnapped the abandoned daughter of the wrong wealthy family. He thought she was asking for money, but she dragged him into a wealthy family to continue being a "toolman". The kidnapper becomes a fake fiancé, and the hostage becomes a partner. Together, they overturn the shady stories of wealthy families, funds, and organs, and see who will be wiped out by this set of rules first.