Right out of the gate this requires the Yasakani Magatama for reduced set req's
The idea is sort of similar to other critical builds in that it uses Fanatic, but here we use Hi-nezumi for the 25% close combat critical attack (the 19% unlimited onmyo is nice as well). Along with Hikoemon Ichimonji for the full set bonus from Fanatic I hold an Oninamida Muramasa for the ninjutsu item recovery when finished with LW.
Hi-nezumi is just another great spirit for critical builds. 25% to critical attack is necessary, and its unlimited onmyo helps keep your carnage, amrita, and pleiades talismans full. I don't use debuffs, and with 20 magic and incantation mastery I can just hit 30 capacity.
I also have 20 dexterity just for flexibility. You need the quick change scrolls which cost 15 for all 3, and tiger running is nice for 6. I went ahead and got incantation mastery for 30 capacity so I run 21 kunai as well. No power pills since carnage overwrites them. This is why the 2 piece bonus from the Iga set is important, it'll keep your scrolls up between LW time.
I like to use the single sword which is why I wear Fanatic armor, you could in theory switch to Sanada if you're using a different weapon for the +skill damage. I don't use skills much with the katana. Keep the Hikoemon Ichimonji for the 30% crit damage though. Using swords gives me a free armor slot so I wear Ogress mask for 20% fire damage. If you're using a different weapon so you have to ditch Oninamida Muramasa just throw on the Iga set headpiece!
That's about it, thoughts?!?!
Edit: Hi-nezumi has A+ in amrita gauge recovery at level 30, I honestly spend maybe 2 seconds out of LW if I'm killing stuff.