To mark the National Memorial Day for the victims of the Nanjing Massacre on Dec 13, origami artist Pei Haozheng released a tutorial on how to fold Zijin Grass, often referred to as the "flower of peace".

During the War of Resistance against Japanese Aggression (1937-45), a Japanese army doctor was deployed to Nanjing, East China's Jiangsu province. When he left the ruined city in 1939, he collected a handful of seeds of a local purple flower blossoming at the foot of Zijin Mountain and brought them back to Japan. He named the flower Zijin Grass, also known as Chinese violet cress and February orchid.

Not daring to mention what had happened in Nanjing, the doctor sent the seeds as gifts to friends and family members and suggested them to plant the seeds in their backyards. In over two decades, every year he would take a train and throw the seeds out of window in hopes of letting these little wild violet-like flowers bloom across Japan.

At the 1985 World Horticultural Exposition in Tsukuba, Japan, the doctor's son donated 1 million seeds and told his father's story to visitors from worldwide. Since then, the flower has been dubbed as "the flower of peace".