America and other countries in the world all have their own superstitions. Some superstitions are worldwide, and some are local to specific areas. There are also superstitions that we think certain places in the world believe in, and then there are superstitions that those places actually really do believe in.
Japan is said to have some of its own superstitions, but depending on who you ask, they may or may not have heard of these superstitions. Some are still alive, and some are just so outdated that you will be looked at weirdly if you bring them up because they are just not used anymore, or maybe never were.
A lot of superstitions have to do with numbers. For example, the number 4 is believed to be an ill-omen because it is pronounced the same as the word “death” in Japanese. So certain things are rarely sold in packs of 4, especially things of a dangerous nature such as knives. You might also find some hotels and hospitals missing a 4th floor in their buildings, the same way tall buildings in the West skip out a 13th floor. It’s just a bad luck number and many people still believe or are at least aware of this superstition.
Giving anything in pairs to married couples is also believed to be something bad. Especially on a wedding day, when giving money as a gift you normally give 10,000 bills in odd numbers. Poorer folks will give one 10,000 yen bill, while most others will give three 10,000 yen bills, with the more generous giving five or seven 10,000 yen bills. But these are never given in even numbers where they can be split.