Reach level 300 or higher
Obtain the Saber Expert title not required
Get the three swords: Saddi, Shisui, and Wando
Visit the Sword Dealer of the West in the Green Zone
Talk to the NPC named Legendary Sword Dealer
Wait until the Legendary Sword Dealer spawns
Buy True Triple Katana for 2,000,000 Beli and 5,000 Fragments