Big in Japan (phrase)

When people say "big in Japan," it means that something is really popular or successful in Japan, like a band or a video game. It's kind of like saying, "They're really making it big over there!" Just like how some people might say, "He's big in Hollywood," it's similar but for Japan. It's interesting because sometimes, things that are popular in Japan aren't as well-known in other places. So, when someone says "big in Japan," it means that whatever they're talking about is a big deal in that country.