FFX - Aeons - Yojimbo

Obtained From
Cavern of the Stolen Fayth
Special Attack
Daigoro - Yojimbo's dog attacks the enemy.
Kozuka - The throwing of a knife.
Wakizashi - A giant slash of the sword.
Zanmato - Chops enemy's head off.
Initial Abilities
Exceed Damage Limit
Get Auron's ultimate weapon, Masamune.

Obtaining Yojimbo

Once you reach the Calm Lands, you can get Yojimbo, provided you have enough gil. About 200,000 should be enough. Go out the exit at the top, and go down the ramp to the right side of the bridge into the valley area below. If you haven't been there before, you'll have to defeat Defender X first. Save, then head into the cavern and go towards the back. There are quite a few nice treasures on some of the side paths that you might want to get while you're there. Once you get to the back, you'll encounter an unsent summoner and you'll have to fight Yojimbo. He has high physical defense, but low magic defense, so using magic is best. I recommend summoning Bahamut and then casting high level magic spells and using his overdrive. This isn't really a tough battle.

Once you've won, use the warp pad to go to the left and right to get some items, and then head into the Chamber of the Fayth. When prompted, choose the third option, To defeat the most powerful of fiends." This will make Yojimbo's asking price 250,000 gil. Offer half plus one gil, in this case, 125,001. He will lower his asking price; raise your offer by one gil. This time he should offer 205,000; you shouldn't go any lower than 190,000. If at any point you offer him triple or more of his asking price, he'll give you 2 Teleport Spheres.

Summoning Yojimbo

As you might've already guessed, in order for Yojimbo to fight for you in battle, you must first pay him. Generally, the more you pay him, the more damage he will do. From what I gather, the amount you must pay him in order to get the different attacks is based on a rather complicated formula. More information on this when it becomes available.