To claim the unique gear available from forts and castles in Assassin's Creed Shadows, Yasuke and Naoe must first defeat the Samurai Daisho.

When you've assassinated both Samurai you can open the Mibuno Castle Legendary chest which can be found on the ground floor of a building in the center of the castle, near where you found the second Samurai. If you're not sure, look for the chest icon on your map and it will show you where it is.

With the best armor in Assassin’s Creed Shadows, Yasuke and Naoe become nearly invincible. As you explore feudal Japan, you’ll find many fabulous body armors, helmets, robes, and headbands, but some are worth wearing more than others — and we’re not just talking about looks.