What is the special meaning of the second button in Japan?

In Japan, there is a custom that if a girl asks a boy for the second button on her clothes and hangs it around her neck with a red line, it means that he is the person she loves most in her life.

This is because it turns out that the second button on the clothes similar to the Chinese tunic suit in Japan is just above the chest, representing the human heart. Whoever owns that button means owning his heart.

In addition, red lines should be hung around the neck and chest to show mutual affinity.

This is the special meaning of the second button in Japan