There were many sad cartoons that could be used as a reference: 1. Qianxun: It tells the story of a girl named Qianxun who grew up in a mysterious and supernatural world. Qianxun experienced many magical adventures while she was lost, but she finally discovered her true existence and purpose. The whole story was filled with a faint sadness, especially when Qian Xun grew up and found herself after losing her parents. 2 Death Note: It tells the story of a talented high school student, Yagami, who created a notebook that could kill people to punish immoral people. The whole story was full of suspense and tension, but it also delved deeper into human nature and moral issues. The relationship between Tsuki and Tomoyo was also very touching. 3. The Grave of Fireflies: It tells the story of a young couple who had to leave Japan to take care of their children during World War II and survive in poverty and hardship. The whole story is full of criticism and reflection on Japanese society, but also shows the fragility and sadness of human nature. Farewell My Concubine: It tells the complicated feelings and life experiences of two Peking opera actors. The whole story is full of historical and political elements, but also shows the pain and entanglement of human emotions. 5. Your Name: It was a romantic story about a pair of young people who traveled through time and space. The story was full of dreams and romance, but it also deeply explored the concepts of time and space and fate, as well as the deep connections and ties between humans.