If I were to hazard a guess, I'd expect it might be somewhere around the Telstra undersea lines getting you over/into Japan. Tracerts may give you a rough idea of where the connection is bogging down. If it's not in the JP subnet that SE owns or the JPNIC portion run by the government, not much that SE can do about it--in such a case, your ISP would be your best advocate.

When I trace to it from here in the states, aside from the usual hiccups around LA, it looks pretty much normal in comparison to what I used to see when I played XI. Both the Asianet and SE lines are holding true to their usual 180-190 response times. So there may be some peering issues with the routing partner your ISP is using to get you overseas. That would be something that your ISP would need to address if it's on their side, or Asianet (by way of SE's request) if it is the interconnect on their end. If the problems are within that routing partner's network, then your ISP needs to take them to task to resolve issues with those segments because your ISP has the enforceable agreement with them to carry your data.