One Piece Episodes Wiki ((exclusive)) -

A bacterial fog makes the crew sick. Chopper synthesizes a cure using the island’s rare flowers, but must fight a giant infected Sea King. Flashback to Hiriluk.

Robin finds a broken Sky Poneglyph on a floating ruin. It mentions the "Fourth Ancient Weapon" (a fake-out – it’s actually a map to a lost library). Sanji protects her from Mist Serpents. one piece episodes wiki

The crew finds a derelict ship flying the mark of the Spade Remnants (a rogue faction of former Baroque Works agents led by a mysterious swordsman). Zoro recognizes the sword style. A bacterial fog makes the crew sick

Zoro duels the Spade captain, who uses a sword that cuts memories. Zoro momentarily forgets Kuina, then remembers her harder, unlocking a new style: "Three-Sword Style: Oath of the Departed." Robin finds a broken Sky Poneglyph on a floating ruin