The 5 yen coin is pretty cool.
Main reason = It has a hole in the center
It’s called a 五円硬貨/Goen kouka which literally means “5 yen coin”.
It’s made of brass and shows an ear of rice, a gear and some water
五円/Goen is a homophone for 御縁/goen which means good luck, especially in relationships.
That’s because go is an honourable suffix and en means fortune or relationships.
This is why the 5 yen coin is often donated at shrines when you pray… it gives you that extra bit of good luck!