BOSS BATTLE: Yojimbo
HP: 30,000
MP: 0
This is not a very difficult battle. Yojimbo will use his Daigoro attack repeatedly at the beginning of the fight. To finish him off quickly, use your aeons' Overdrives.

Before you step on the teleport pad in the room, be sure you have at least 250,000 gil. You can warp to the left and the right to get a few valuable items, but for now, go straight ahead into the Chamber of the Fayth.

Now it's time to bid. If you ever triple his asking price, he'll offer two Teleport Spheres as well, so keep that in mind. He'll give you three options at the start; pick the third, as it causes him to give his lowest asking price (250,000 gil). Don't bid the whole lot, yet, however; bid half his asking price, plus one (if you picked the third option, that would be
125,001 gil). Raise your offer by one gil each time to lower his asking price. Once his price gets to 205,000 gil, that's about as low as you can reliably take him, so bid around 190k-200k to get him in your party.

Unlike the other secret aeons, Yojimbo cannot initially break the damage limit. You must acquire and power up Auron's ultimate weapon, the Masamune, to allow Yojimbo to exceed 9,999 damage. To do this, you need three items: The Mars Crest, the Mars Sigil, and the Masamune itself.

The Mars Crest can be found in the Mi'ihen Oldroad. Head to the end of the Highroad, to the junction before Mushroom Rock road, where you met Seymour for the first time before Operation Mi'ihen. Get a chocobo if you like, and head down the lower path. Follow this path all the way to its end, and there you will find a chest with the Mars Crest.

To obtain the Mars Sigil, you must unlock any ten Area Creations or Species Creations. Just catch complete 1 area of catching with ten full monster Besaid is the easier so get there first.

The Masamune, the final piece, cannot be obtained directly. First you need the Rusty Sword, which is found on the path just east of the entrance to the Cavern of the Stolen Fayth. Once you have this, return to the junction between the Mi'ihen Highroad, Mi'ihen Oldroad, and Mushroom Rock Road. Go into Mushroom Rock, but instead of going left as you did when you came through to Operation Mi'ihen, go straight. You will see a path to the left on your map. Go into it and ride the elevator up to the statue of Lord Mi'ihen standing over a slain Behemoth. Press X in front of the statue and you will place the Rusty Sword. If you have the Celestial Mirror in your inventory, you will receive the Masamune.

Special Attacks:

Yojimbo's repertoire of attacks is far lower than most other aeons - just four. However, they are all quite powerful, especially if you max out his strength. Wakizashi is probably his best attack, when comparing attack strength and gil economics. If you've got the gold, however, Zanmato is an instant kill to anything.

-Daigoro-
Yojimbo's dog, named Daigoro, attacks the enemy. This can be done for very
little gil, but it is weak.

-Kozuka-
This is Yojimbo's 'Three Daggers' attack. He withdraws three small daggers (kozukas) and hurls them at the enemy for moderate to high damage. This is also a fairly cheap attack, and Yojimbo will reliably perform it for anywhere above three hundred or so gil.

-Wakizashi-
Yojimbo withdraws his sword, ironically called a wakizashi, and slashes the enemy for high damage. This is arguably Yojimbo's best attack, because it can be reliably performed for one thousand or greater gil, and it also reliably does 99,999 damage at full strength.

-Zanmato-
The infamous, elusive Zanmato, which roughly means "Demon Edge" in Japanese. Yojimbo calls a sword up to his hands and attacks the enemy at blinding speed, slicing them in half. This is an instant kill to ANY fiend, including ALL bosses, even those immune to instant death. It is also insanely expensive, even if you have high compatibility with Yojimbo. There is a slightly higher chance of Yojimbo performing Zanmato if his overdrive meter is full.