Age of Empires IV: Anniversary Edition

From what I can find from trial and error this achievement is a reasonably slow and painful grind taking a few hours just for this one achievement! However, here is the fastest method I have found!

Firstly, start a 2v2 skirmish playing as the Japanese with;
1x Easy AI ally
2x Intermediate AI enemies.
Map: Mountain Pass
Fog of War: Revealed
Starting Age: 1
Starting Resources: Maximum

The Ozutsu unit can only be produced by the Tanigashema Gunsmith from the age 4 military landmark.

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There is a bit of setup to aid things;

1. Split your workers, half will build up your base in the corner of the map, building the essential landmarks needed and research buildings.
2. The second half will immediately go to the opening in the mountain pass and start building a massive defensive wall section between the two!
3. For my defensive wall I used a wooden wall with 3 gatehouses; immediately behind that was a solid wall of outpost towers; further behind that (leaving a small gap) was a stone wall which I furnished with gates and stone wall towers at every other spot; immediately behind those would be castles. This is our defense so we can focus on hunting siege units.
4. When you build the Age 4 landmark, place it just behind our new wall in the center of the map, also add ample barracks, archers, and more as we will need a regular army as well. The latter will likely need to be continuously producing Ozutsu units from the get-go!
5. Create two armies in front of your giant wall, an army made up entirely of approximately 70-80 Ozutsu's units and the remainder army made of a medley of all units supported with a few siege items of your own.

Screenshot of my army setup!
https://1drv.ms/i/s!AnQm6R3RSwOEgeZALiaL_wdKGl0-3Q?e=1Nx02K

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Now the game should be set up! it may take a little while to get to this point as you will now and again come under attack from the enemy!

Your Ozutsu units are generally terrible at taking down enemy siege units and take a long time to kill each one. I would also recommend waiting for the enemy to come to you with a large force complimented with 5-6 siege units rather than hunting their base as your lone Ozutsu will get torn to shreds.

1. Watching the enemy, eventually, they will attack your wall, normally the extreme left or right (I got picked on a lot from the right and barely the left-hand side. When they attack, wait till they're getting close to your wall and counter their front units with your medley army so they don't destroy too much of your wall.
2. With your Ozutsu army, flank wide around the rear and try to get behind the siege machines before they quickly decide to retreat.
3. Clear the frontal enemies and retreat your medley, with your Ozutsu's, destroy as many of their sieges as you can, you'll likely only get 1, maybe 2 if you're lucky!
4. Now, if you have enough Ozutsu you can use your troops to block the enemy movement rendering them unable to move by clicking and moving your troops to their location. If you can get the placing right you can trap 3-5 sieges within your troop's area, they will simply stop or spin in circles. Now you're free to slowly pick off the remainder one by one.
5. Once you've completed the wave, return your troops to in front of the wall, rebuild/repair any structures, and replenish your armies as necessary. Now wait for the next wave to appear and chip away at that progress!

Example screenshots of getting them stuck!
https://1drv.ms/i/s!AnQm6R3RSwOEgeY_aWk4p3_Zelw7cA
https://1drv.ms/i/s!AnQm6R3RSwOEgeZBPTf4Ie-vvGUDew?e=819Wga


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