Reach 100% Growth on Swords, Spears, and Bows to unlock super weapons.
Successfully complete the game to have unique weapons from the Dynasty Warriors and Samurai Warriors series appear for purchase in the shop. These include Nobunaga's sword, Guan Yu's halberd, Zhao Yun's spear, Xing Cai's pike, Xiahou Yuan's club, Yukimura Sanada's spear, and Magoichi Saika's gun.
Durandal
Successfully complete the game as France to unlock the two-handed sword Durandal (Edge: 99, Point: 99, Blunt: 99, Magic: 99, everything else 0).
Easy experience
In your very first contract you will have a tutorial on how to use swords, horses and bows. When it tells you to use the Bowmen, do not take control of them. Instead, use the Swordsmen to fight the groups of people. After fighting for about a minute you should gain a level. You can do this as long as desired to better your men, making the beginning of the game easier. You can switch to the Horsemen to also increase their levels. When you feel you have their levels high enough, switch to the Bowmen to finish the tutorial.
Excalibur
Successfully complete the game as England to unlock the single handed sword Excalibur (Edge: 99, Point: 99, everything else 0).
Shop discount
Collect all twelve Gems. You will unlock a short intermission sequence featuring the merchant and the shop's prices will now be discounted.
Unlimited Ammo
With any unit that has ammo (Archers, Javelins, Throwing Knives, etc), wait until you are out of ammo. Press X to back out of the unit, and wait for the AI to shoot of their own accord. Re-join the group, and you should have about 10 more ammo, which is not a full restore. When you run out, just leave the squad, wait, and re-join. It can be done infinite times.