Whereas in a lot of Western countries we would prefer to be the only one to wear a certain piece of clothing and being in the same place as someone dressed exactly like us is not desirable, in Japan, it is a bit different.
In Japan, it is not rare to see couples, family or friends dressed exactly the same, it is something that is called osoroi code in japanese (おそろいコーデ from the English coordinate). For Japanese, it is a way to show their affection to the persons they are with!
It is something very popular with youngster and you can qnd you can sometimes see some people dressed the same way in some areas, especially in Harajuku .
If you want to try it and do not feel confortable with the idea to be dressed exactly the same as the people with whom you are, you can try Disney Land Tokyo or Disney Sea where you will find a loooot of people dressed in osoroi code