Become an Emperor by Exchanging Books

He became a cowardly cannon fodder through the book, assassinated the emperor to avenge his family, but switched bodies with him. After the regicide failed, she became the emperor, but the original emperor was thrown into a water prison and became a favorite concubine. The two were forced to cooperate for a short period of time, using each other to solve each other's problems, only to discover that the other party's methods were amazing. She used her charm to stabilize the situation and win by surprise; he used his iron fist to revenge and protect her.