It’s much more than Japan: Chinese in other countries, Philippines, etc. I’ve met in person sons and daughters from “second families”.

Also the French, so it’s not exclusively a practice of East Asian people.

You literally have cities in China that are called "second wife villages"(二奶村) where politicians and rich people have their mistresses that are located close to ports/airports for quick access on "work trips". In Shenzhen for example its the Luohu (罗湖) and Futian (福田) districts that are for this purpose.

It's a bit much to say the purpose of Luohu is mistresses, but you're right that it definitely is not a Japanese-specific thing.

Might be but last time I checked Huang was not Chinese.

Correct, and OCT (also in Shenzhen)

Don't make it sound like Japan either. It's just not possible where no family with a connection to someone powerful would be satisfied hidden away in a rural village. When caught by a tabloid, your career ends completely, not really excepted behavior.

Confident much or are you playing on concubine vs wife game word?