From here on out, you can't use Warp or Exit to leave quickly, so be careful. The enemies here are worth plenty of experience, but they are also very nasty. You'll find the Fuma Shuriken along the path. At the southern end you'll see a floating sword like the Murasame. This is the Masamune, and it's guarded by Ogopogo, basically an upgraded version of Leviatan. He'll open the fight with a double Big Wave, so make sure Rosa is ready to heal. (Giving her the Sage Staff will help in this regard.) Ogopogo will counter magic and summons with Blaze.