Japanese coins have holes in them for practical reasons. The first Japanese coins, called wadokaichin, were minted in the late 1600s and were made of copper. These coins were quite heavy and difficult to carry around, so people began to punch holes in them and string them together for convenience. This made it easier to carry large amounts of money around and prevented the coins from getting lost.
Over time, the holes became a traditional feature of Japanese coins and were included in subsequent designs. The 5 yen coin, for example, has had a hole in the center since it was first minted in 1870.
In addition to practical reasons, the holes in Japanese coins also have cultural significance. The circular shape of the hole is said to represent the harmony and balance of the universe, while the square shape of the coin represents the earthly realm. The hole is also believed to ward off evil spirits and bring good luck.
Overall, the holes in Japanese coins are not just a unique feature of their design, but also a reflection of the country's cultural and historical traditions.