~Obtain Yojimbo~

This trophy is obtainable once you reach the Calm Lands. After leaving the Calm Lands but before reaching Mount Gagazet you'll have to cross a bridge and there will be an alternate path under the bridge. Go down this bridge to a new area and there's a cave entrance near a save sphere; it's inside this cave you can obtain Yojimbo. There is some story with this cave, but there are also plenty of fiends so be aware of their presence. Once you reach the back of the cave you'll enter into a fight against Yojimbo himself.

Yojimbo isn't that powerful as long as you have a good defense stat; he himself has a good defense stat and a weak magic defense stat. The only thing to watch out for is if he gets a full Overdrive Meter you will have to have Yuna come in and summon an Aeon to take his next attack. Once Yojimbo is down, use the teleporter and have it move you north (up) to the Chamber of the Fayth.

Warning: Before you negotiate his price, Yojimbo will want to know how you'll use his power; you have three options available to you. If you plan to use him in the end game, select the third option which is something like "To defeat the most powerful enemies." What you choose here determines his likelihood to perform a Zanmato powerful enough to take out powerful enemies. Even if you don't plan to use him for the end game, it's the best option.

After answering his question he'll want you to pay him for him to join you; you can negotiate him lower but be careful because he will refuse you if you go too low. He first quote is 250,000 Gil, which you can cut down to 125,001 Gil. This will get him to lower his price to 225,000 Gil; you can cut it down to 112,502 Gil. This will get him to lower his price to 202,500; from here you can undercut but not a lot. Some claim to have gotten him down to 180,000; but I was never that lucky. If you undercut his third offer he'll turn you down and you'll have to renegotiate the price again; if you offer enough he'll join you and you'll earn this trophy.

See the Yojimbo FAQ if you plan to use him in the end game.