Version 1.0 on 2/24/2013 - Completed and double-checked.
Version 1.01 on 2/27/2013 - Mentioned Kill ratios in the siege section.
Version 1.02 on 3/12/2013 - Made a mention on preventing rebellions in the intro section. Gave some more minor information on the intro section.
Version 1.03 on 3/13/2013 - Added more info in the siege section.
Version 1.04 on 3/18/2013 - Added more info on stratagem 1 & 2.
Version 1.05 on 3/21/2013 - Added achievement percentage in intro.
Legendary mode is border-line impossible at first. The enemy is basically cheating. They use ant-like tactics to win. They will continually send wave after wave of grand armies (Zapp Brannigan). At first, they just throw grand armies full of ♥♥♥♥♥♥-garu units. Then they'll start sending in the katana samurais, monks, heroes, and a bunch of other stuff won't normally see on easier difficulties.
For this guide we used the Shimazu clan for their Katana expertise and the Otomo for their early access to superior gunpowder units/ships. The Otomo clan isn't normally available but it can be yours... for a low, low price of $4.99.
My buddy, Firemagzz (Otomo), and I have lost several times playing with different factions. We eventually started to realize that we needed to consolidate as close as possible. Which is why we chose these two nut-to-butt clans. Also, they compliment each other nicely when it comes to melee/ranged units.
Creative Assembly did not test the coop function properly and you WILL (95% of the time) experience desync problems which will be catastrophic and irreversible. The only way to combat this is to back up your multiplayer auto save every now and then at:
C:/YourUserName/AppData/Roaming/The Creative Assembly/Shogun2/save_games_multiplayer.
If you didn't do this, and you're having desync problems, you can switch your saves, so that you're both using either the host's save, or the client's save. This will buy you some time until the desync problems occur again.
This challenge is certainly for those with at least 30-40 hours of time, and this is the short campaign! Take note that at this time (3/21/2013) only 0.9% of all Shogun 2 players have this achievement.
With all the resistance, your advance will be slowed to a snail's pace. Patience and calculated risks are the key. My guide will lay down the foundations of the grand strategies you will use. You must employ these seven samurai stratagems. If all else fails, you must alt + F4 and reload the save.
These are the seven samurai stratagems:
1. The Siege Slaughter strategy
Forts/castles are essentially meat grinders. With one grand army in a fort, you can easily kill 2 grand armies in a siege battle and with minimal casualties. Against a force equal to my army's size (40% in my favor), I would normally get a kill ratio of 4-5. For every man the enemy killed, I would kill 4 of his.
The key to siege battles is to never attack the enemy and let them always attack you. This usually happens if you continue a siege for a while (offensive) or if the enemy army is more powerful (defensive). You can then counter-assault when they are vulnerable and you are not. If you need to directly siege a castle at full enemy strength (like Kyoto), you must have double their strength and a lot of katana samurais. Any less than this, and it will be suicidal. Once you take their city, you must occupy peacefully. Sacking causes a lot of problems and its short term gain is not worth it.
When you are being sieged, you will take some losses despite no fighting taking place. Also, remember this following equation. Gunners behind walls = death. Bullets don't care about unit quality or armor. Gunners will kill about a third of an entire unit before they reach the walls... that's IF they reach the walls. If by the off chance they do reach the walls, you must move your gunners back and let your katanas slaughter the enemy. In one siege, I was outnumbered 3 to 1 and took massive casualties (72%) but lost one unit card. The enemy was in shambles and lost 82% and several family members. Thanks to my upgraded encampments, it's like the losses never happened in the next turn.
After the battle, you should be replenished in 1-3 turns, thanks to the encampments, and you should have more veterancy, which is key. You must be careful and not let your super elite units be wiped out. Rarely will you be sieged to surrender.
Don't forget to use your Stronghold's guard tower's fire arrows ability.
Also, on an offnote, Bow Samurai are effective against samurai units while Bow Ashigaru are not very effective. If you are taking a lot of arrow fire from outside your castle, just move your units to the farther into the castle. Once you are out of the enemy archer's range, they will move closer to the castle and possibly climb the walls. Or you could just go out and kill them. Just try not to stand there and take archer fire.
2. Research Heaven and Earth
This is the most important Bushido art and overall art you will have. You need this to build encampments (improvemented replenishment rate). Replementment rate is almost nonexistant without encampments. You need to have these in order to be able to withstand the onslaught of ♥♥♥♥♥♥garu armies. If you're going to be in realms divide, you better upgrade all encampments to barracks for further replenishment rate. To maximize your replement rate, you can also upgrade your forts and your roads.
3. Economics & Politics
Make sure your forces are stretched to the limit. At the end of the game, I had 5 grand armies with no garrisons in the rear. This will help you save a lot of money. Also, you need to have 10 trade ships in every trade port you can get. Normally, the computer won't attack the 10 trade ships. They'll attack 1 trade ship but not 10 normally. As for trading, link up with Otomo in land and try to trade with only people from far away, as they are less likely to attack you. Trading also helps improve relations in the long run. Also, you must make sure you don't get blockaded as it will destroy your income.
Research mainly economics like the farm upgrades, tax upgrades, market, sake den, etc. And when you upgrade farms, you have to upgrade the fertile soil first before the meager soil. The cost is the same but the results are vastly different. After this, you have to research happiness and repression to expand faster.
Repression forces you to slow your invasion down. As the Otomo, you have to build chapels to repress the religious rebellion. As the Shimazu, you have to build buddist temples in territories adjacent to the Otomo to prevent Christian uprisings. No taxation, monks/ missionaries, and yari ashigaru units will help prevent rebellions. Try to keep the predicted repression on at least 0. If you exempt a region from taxes, don't forget about it. A quick look at the happiness map at the end of every turn should prevent you from forgetting this.
There is no need to adjust the overall taxation rate and it is not recommended.
If you have no problems, try to build wealth buildings. Farms, markets (if you have enough food), and then everything else.
As the Shimazu, you must upgrade your blacksmith to the maximum melee capacity at your capital and you must produce katanas only here.
The enemy should be fractured east of Kyoto. So you don't need to worry that much about those clans. You should strive to maintain peace with as many people as possible, if profitable. If a warring faction asks for peace, you can counter-offer that they pay you thousands of koku. They normally will say that it's satisfactory before you click the accept button.
Try not to betray alliances. It soils your Daimyo's honor, and it hurts your diplomatic standing badly, which could be bad for peace, repression, and trading.