Shadow Tactics: Blades of the Shogun - Aiko's Choice

At the start of the third level (Toba Coastline / Best laid plans) Switch to Takuma and move him closer to the edge of the crow's nest (towards the front of the ship) and use his weapon to kill the captain below. He is labeled as a "straw hat" and has a different outfit compared to everyone else on the boat (frills around his neck).