The Iron Umbrella is a useful Shinobi Prosthetic Tool that will allow you to block incoming damage. It can be especially useful against enemies that induce Terror. If you want to get your hands on it, you will need to find Blackhat Badger in Ashina Castle.
Where To Find Blackhat Badger, The Iron Umbrella Shinobi Tool
The easiest way to find Blackhat Badger is to use an Idol to travel to Lord Kuro’s room. If you don’t have access to Lord Kuro’s room, you are not far enough into the story yet to need this item. As such, play through the story until you do arrive there. Once you get to Lord Kuro’s room, use the window to move out onto the roof of Ashina Castle, walk around the back of it, and jump off into the pool there. Swim to the dock and jump up, then move through the large gate. Take out the two guards then move ahead to the Idol.
Now, take the right staircase and begin to work your way down the steps. Be careful, there are a lot of enemies here, including some guys with cannons. Take them all out, and as you reach the bottom, you will find a pagoda with a broken wall. Jump up to the roof, then drop down into the hole. Here you will find Blackhat Badger. You can purchase the Iron Umbrella from him for 1600 Sen. After that, bring it to the Sculptor and he will add it to your Prosthetic Arm.
There is also a lot of loot to be found in this area, so make sure you have a good look around!