Before you can start making strong weapons, you need to have played Ambition Mode first and make sure you have gathered enough materials so you can upgrade the Blacksmith Shop. Weapon and Facility Materials can be gathered by playing the Skirmish battles.
1. Blacksmith Shop to Level 30 or above.
2. An empty 3rd or 4th weapon.
(Empty 3rd weapons can be acquired by buying them in shops on Normal mode, I suggest playing Wei's Chibi stage. The empty 4th weapons can be bought in shops by playing on Hard difficulty although they are notoriously difficult to find, I suggest playing the Campaign for Jianye stage - Wei side).
3. Weapon Materials over 150
4. Weapons that only has ONE skill on it - here are the skills that I recommend to increase the chance of critical damage.
*Slash - Inflict additional damage against the enemy or even defeat them in a single blow.
*Explosive - A powerful shockwave may be unleashed following a successful attack.
*Velocity - Increase your attack speed.
*Cyclone - Inflict some damage on even enemies that are guarding.
*Flash - Cause enemies that have accumulated damage to explode
*Recovery - Your health Gauge will recover somewhat with each successful attack. (I recommend this for fast killing characters + Cyclone, or if you dont want too much life heal and you want to challenge yourself on chaos)
*Jubilation - Recover a portion of your health gauge when you defeat an enemy. (I recommend this for characters that has slow attacking speed. This skill activates on musou/rage attack. Very useful on overpowered set ups!)
*Induction - Lightning may strike the enemy following a successful attack.
*Fury - Able to use True Musou Attack.
*Any of the other elemental affinities - Inferno, Thunder or Frost.
5. You will need at least five 3rd or 4th weapons that has skills on them over +4 to +8. This will increase the input of the skills you have stacked on the weapon.
NOTE - SOME CHARACTERS WILL NOT HAVE ELEMENTAL ACTIVATION. Here are the characters with no elemental activation on their charge attacks - WILL BE UPDATED.
Li Dian - Only his final square string has elemental activation.
Cao Cao - Only his final square string has elemental activation.
Lu Xun - Only his C3 and final square string has elemental activation
Sima Yi - Only his final square string has elemental activation
2. Make sure that you find another weapon that has one of the skills above. So this time we will add 'Slash'.
4. After adding all the skills you want on the weapon, it should look like this:
5. The skills on the weapon cannot be replaced with other skills, it is permanent, so before tempering make sure you have thought about the skills you want on the weapon!. You will then have to stock a 3rd or 4th weapon that has skills on +4 to +8.
Where to buy strong weapons - Play Shu's Hypothetical Route, Capture of Wei. Pick 'Play All' and go on Chaos difficulty. You can pick any characters, it wont affect the skills of the weapons in the Blacksmith Shop. You should be able to buy powerful weapons which you can then use to stack on the weapons you are tempering. When you got all the weapons you need, save it and soft reset.
6. This stacks the skills on Zuo Ci's weapon, making it more powerful. Remember that the skills wont be replaced.
7. Keep stacking more weapons until all the skills are on +10. Here is an example of a fully stacked weapon.
NOTE - NOT ALL SKILLS CAN BE STACKED TO +10, AN EXAMPLE IS FURY.
And there you go, a fully stacked weapon! You can now destroy everything on chaos and maybe OHKO Lu Bu!
Credit to Wynter , Source: Koei Warriors Forum