Nippon TV created the original Money Tigers format adapted into Dragons' Den.
Money Tigers was a Japanese television programme developed by Nippon Television Network Corporation, commonly known as Nippon TV. In the format, entrepreneurs sought investment from wealthy businesspeople, creating the model later used by Dragons' Den and related shows.
The British programme is therefore an adaptation rather than an entirely original concept. The format travelled internationally under different names, most notably Shark Tank in the United States, while keeping the central idea of entrepreneurs pitching for equity investment.
Nippon TV is distinct from NHK, Japan's public broadcaster, and from other commercial Japanese networks. Those broadcasters are plausible but incorrect alternatives because Japan has several major television companies.