Thanks for all the info. Sounds like I can skip level 5 anyway which will help a bit on the tedium. I had already spent a bunch of time farming there when I still needed some of the rings.
I don't plan on using most of this stuff (like the control seal), I just want them for my collection. Though I would really like a decent weapon for my samurai, which is why I have been focussing on the muramasa for a while now.
Btw, sorry for the weird errors in my previous post. I was writing it in a hurry from work and didn't have time to proofread it. Looking back on it now, I've got two entries for Mjolnir, the second of which makes absolutely no sense
I think was talking about the Control Seal but mislabeled it, since both drop off Black Dragons. And since you're going to kill so many on Shiin 10F anyway, it'll pop up like a Mjolnir in your bags before you know it.
Keeping my previous post in mind, your primary farming target for right now should be one of the insane katana upgrades. Doesn't matter which one. Murakumo is easiest to come by if you can handle the Daemon Lords, otherwise try for a Bizen Osafune since Musashi rarely shows up with additional enemies.
Once you get one of those katana (and they're all so powerful it doesn't matter which), it becomes an entirely new game since you can essentially farm huge packs of enemies using Sougeki-Hamon no Jin in seconds. The Sacrificial Seal also completely changes the game, though in a very different way. If you've got the seal and one of the three super katana, Lost Souls changes from a dungeon crawl to a monster genocide simulator, loot rains from the sky, and you only ever have to go back to town to warehouse your new toys.
"Staring at the sea, staring at the sand ..."