Italian words are divided into feminine and masculine. Here are two words "ASSOCIATION Club" and "INTERNAZIONALE International", both of which are feminine. The former feminizes Italian football. For example, we are familiar with the words "Seven Sisters in Serie A" instead of the seven brothers in Serie A, "old woman" (meaning elegant, not "old woman" or "March 8") and "red, black and beautiful" all have feminine meanings. The latter gave the feminine club Inter Milan a feminine name, so the great international of the 1960s was called the "Queen of Europe" instead of the European emperor. In this way, the "sister" of the word "cousin" can be qualitative, at least not called cousin or cousin.
Since the 1960s, Milan once won the championship, and the fans shouted "We are champions". At this moment, international fans shouted at each other, and your champion was cheated. Milan fans are unhappy. At this time, someone shouted, "We are champions, and you are cousins of champions". Soon, Milan fans unified the slogan, "We are champions, and you are cousins of champions". So the name "cousin" was handed down. If you don't believe me, go abroad. This has become a standard name for 40 years.
There is also a saying that Inter Milan was once "bullied" by Milan. When they lost, they complained to the media. The media was nicknamed "cousin" by Italian fans, so it was of course my cousin who cried and complained to "cousin dad".
As for Manchester City, I think it may have been invented from it. Learn from Milan's name for Inter Milan, so it's always been called that. Manchester United fans associate it with the beautiful Manchester City and learn to shout like this.
Brothers and sisters who want to know add it.