The Six Blades of Kojiro is an Umugi Mythic Tale in Toyotama, where you duel five Straw Hat assassins and then Kojiro himself. It has more duels than any other single tale, and it rewards the Kensei Armor, a set that boosts Resolve and Ghost Weapons.
Part 6 of 9 in Mythic Tales
Kojiro was a Straw Hat ronin so savage that his own brothers turned on him. He killed all of them in a day-long fight, and the spirits of death blessed his armour. Now the Straw Hats have taken him back, and five of their killers have sworn to kill you.
You can take them in any order. The flower field is the Field of the Equinox Flower. Yasumasa waits below Old Kanazawa Marsh for the Duel in the Drowning Marsh, and uses a hostage as bait. Hirotsune, who boasts he has held a sword since he could walk, waits among spider lilies on the north side of that flower field. Kiyochika plays a flute behind a waterfall over the Musashi Coast. Tomotsugu fishes on rocks under Cloud Ridge Shrine, in the Duel of Crashing Waves. Kanetomo, who has been killing innocents, sits beneath autumn trees to the east of Yamabushi's Peak.
After all five are dead, go back to Yamato in Umugi Cove. He tells you Kojiro is waiting at Omi Monastery. Enter the grounds and search the rock face for a cave mouth; the Guiding Wind helps if you get stuck. Talk to Kojiro, then win the last duel.
The Kensei Armor raises Resolve gains and Ghost Weapon damage, and weakens anyone you tag with a Ghost Weapon. At tier I it looks a lot like the Ronin Attire, and later tiers add a cape. It has a fifth upgrade in New Game+.
The Spirit of Yarikawa's Vengeance
The Spirit of Yarikawa's Vengeance is a Mythic Tale in the Ruins of Old Yarikawa, Toyotama. You follow offering shrines to a vengeful spirit and learn the Dance of Wrath, a three-hit unblockable katana technique.
The Unbreakable Gosaku
The Unbreakable Gosaku is a Mythic Tale that starts in Akashima Village, Toyotama. You free six farmsteads to collect six keys, then open a hill in the Old Togo Rice Fields to claim Gosaku's Armor, a tanky set built around Staggering enemies.
The Curse of Uchitsune
The Curse of Uchitsune is a Hiyoshi Mythic Tale in Izuhara, where you search for a legendary archer's cursed bow. Finishing it gives you the Longbow, the longest-range weapon in the game, plus Explosive Arrows.
The Heavenly Strike
The Heavenly Strike is the first Mythic Tale, set in Komatsu in Izuhara. You hunt a killer who wants Shigenori's legendary sword technique, and finishing it teaches you the Heavenly Strike, a fast unblockable katana attack.