Things You'll Need
Instructions
Defeating Chac with Zantetsu
Travel to Via Infinito floors 50 to 59 and battle Jumbo Cactuar's until you have collected six Rabit's Foot accessories. The Rabit's Foot is the Jumbo Cactuar's rare drop, so it may take awhile to collect six. You can collect one less Rabit's foor for each Bushido Tome that already have. Teach each of your heroes the Thief Dressphere ability First Strike and the Samurai Dressphere ability Zantetsu during your Cactaur battles.
Equip the Thief Dressphere and the Samurai Dressphere to the Ray of Hope Garment Grid. Equip each member of your team with the Ray of Hope garment Grid and two Rabbit's Foots each. Bushido Tome will also work. Equip each character as a Thief. They have First Strike active.
Save your game in the Cloister of Trials just outside of the room where you encounter Chac. This may require multiple tries.
Seek out Chac. Once the battle starts, your characters will act first because of First Strike. Have each of them change dresspheres to obtain the Luck Bonuses of the Ray of Hope Garment Grid. They must end as Samurais.
Attack with Zantetsu. Because your luck is maximized, Zantetsu has a strong chance of instantly killing Chac. Armed with three Samurais and three Zantetsu strikes before Chac has a turn to act, the odds are still not in your favor. Reload the game and repeat steps 4 and 5, if your party wipes out. You should prevail within three attempts.