How to Obtain Lady Noh's 5th Weapon in Samurai Warriors

Farm some good items. You will need a good Solar Gem, Moon Stone, Power Bracer and Himiko's Rune for this. Ideally, a +30 or better bonus is what you're looking for.

To farm equipment, play Mitsuhide Akechi's Betrayal at Honnouji stage on Hard or Chaos difficulty. Play as Mitsuhide, equip a saddle (ideally a Matsukaze) and run around collecting items. As long as you don't die, the stage will be completed and you'll walk away with some great gear!

Get a speed boost. In case you don't already have it, get yourself the Matsukaze saddle or a good pair (30+ bonus) of Tengu Sandals. Noh is naturally fast, but these just serve to make her REALLY fast.

Reset if you need to. If you have already tried to obtain this weapon and failed, reset Noh's stats. This will make the enemies comparatively easier.

Bring your friend! Fighting on Hard difficulty is always easier if you bring a friend. Remember though that the opponents difficulty is based on the average level of both you and your companion. If both of you are very powerful, the opponents will be as well. If you both reset your characters to level 1, the opponents will be considerably easier.

Let the battle begin! Start Noh's Betrayal at Honnouji stage on Hard difficulty. This can be done on Chaos, but why would you want to?

Head south to defeat the Defense Captain, then go after Nobunaga.

Kill your husband, the demon lord Nobunaga. He is strong and fast, so give it your all.

Head southeast. Once you kill Nobunaga, you should get a message telling you a Supply Team has appeared. Ignoring all else, head to the southeastern gate and wait for them. Eliminate enemy generals once you get there, if you can do it quickly.

Defeat the Supply Captain for your weapon.

Finish defeating officers, paying special attention to Mitsuhide. He is extremely dangerous!

Finish the stage as normal. Congratulations!