The keychain represents the round window under the "fake Totoro reception" at the entrance to the Ghibli Museum, where you can see many Makkuro Kurosuke. This window, called the "diving window," is a popular spot in the museum, and people who spot it just can't help but stop and stare. By wearing a reflector, the light reflected by car headlights will make you more visible to drivers. This keychain is easy to wear anywhere and is recommended as a safety item.
