Yahoo! Japan was a joint partnership of Yahoo! and SoftBank. From what I could tell while working at Yahoo!, Yahoo Japan was able to use whatever software they wanted from Y!, but whatever they developed wasn't accessibly by the rest of Y!

So, they had their own installation of geocities, and didn't need to take it down. Yahoo auctions is also big in Japan, but was killed everywhere else. (Edit: change was to is)

Yahoo Auctions in Japan is still the market leader today! :P

Sorry, I've edited, I left Y! a while ago, and didn't follow the japanese auction market, so I wasn't sure if it was still the leader.

I think Mercari has a legit chance of catching them, but YA is definitely the leader.

You know you've made it when you get a Truncation nickname in Japan (sort of like the Hollywood couples names like bennifer) "yafuoku"

Yahoo Japan is probably the only Yahoo anyone (willingly) uses. E.g. Yahoo! Auctions is the equivalent of eBay here.