Nissin is a Japanese manufacturer of flash units. It differs from almost any other Japanese company I've dealt with by having poor communication skills, not responding to customers concerns, and putting stuff on the market before it is ready. Its manufacturing facility is located in Shenzhen (China) and its sales operation is located in Hong Kong. For all practical purposes, I would say that this is a Chinese company.
The company was founded in 1959, and has produced professional flash units since 1967. In 2007, the company introduced Di622, its first dedicated flash aimed at the DSLR TTL-market.