During Japanese festivals there is a custom of avoiding the usage of certain words, such as cut and tear. However, the most popular present, the letter is associated with these taboo words. This “ceramic case for letter” is to be opened with a hammer, similar to the action of kagami-biraki*. This is an envelope that gives color to your special anniversaries, which happen only once in your life – just like the ceramic envelope that cannot be the same once it is cracked open.
Cracking a wooden cover of Japanese alcohol barrel with a hammer in celebration days.