Shanghai Agreement Office

In Shanghai in 1925, the Tianchan Stage caught fire inexplicably, and the troupe leader Mei Lanting died in the flames to save Mei Yingxue and other apprentices. Many years later, the arrival of new legal advisor Qin Mo caused Mei Yingxue and others to start a new investigation. What is the purpose of Yamaguchi? What does Mei Yingxue's tattoo mean? What do the words in the notebook mean?