Basically, Yojimbo's attacks suck up your MP dry, and his Zanmanto brings down every character's HP and MP to 1. However, you do not need MP to win this battle, it is not in anyway required, I didn't consume any. In this case, an Alchemist comes in handy, I made Rikku my Alchemist, Yuna my Gunner, and Paine as a Dark Knight. If you don't have Dark Knight, then it'll still be easy for you, it'll just be moreorless time consuming. So for Yuna and Paine, or whomever if you feel like using someone else for an Alchemist.

The key abilites in this battle are Rikku's Mix ability, Yuna's Trigger Happy, and Paine's Darkness attack with the Dark Knight dressphere. For me, Paine's Darkness took away the most for me, Trigger Happy is ok, but just use whatever you feel takes away the most damage.

In the beggining, have your alchemist use a Chocobo Wing to haste the entire party, or just a Chocobo Feather, as long as the Alchemist goes into haste, the battle does end quicker if the entire party is in haste. If your HP drops low, have your Alchemist mix a potion and a high potion to form a mega-potion, which recovers 2000 HP for YRP.

The key in this battle is to wait for Yojimbo's Zanmanto attack, while he's using it (during the animation of the attack, not before) have your alchemist IMMEDIENTLY mix a potion and a high potion to bring your HP up, again, MP does not matter as long as you're using Trigger Happy and Darkness, if it does, then it shouldn't be that big of a problem anyway. Even if you don't get the mix off in time, you can still come back, so don't give up.

Anyway yeah, pretty easy. I'm sure a lot of people felt that it was easy, but I just felt like posting this for those that were having probs.