There are four Bamboo Strikes in the Iki Island Expansion for Ghost of Tsushima: Director’s Cut. These are completely optional but if you’re aiming for all Trophies, must be completed towards that goal. These will also offer an increase to Resolve.
Tatsu’s Ladder Bamboo Strike - Northeast of Katayama Market
Fast Travel to Katayama Market and head northeast towards the river to spot this Bamboo Strike on some raised ground.
Shipwreck Bamboo Strike - Yahata Forest
Make your way to Yahata Forest and head to the northeast corner to find this Bamboo Strike near the shipwreck.
Buddha’s Footprints Bamboo Strike - East of Shrine in Shadow
This Bamboo Strike is located towards the far south of Iki Island, at Buddha’s Footprints. If you’ve already located the Shrine in Shadow, it’s just a short distance to the east of it.
Saru Island Bamboo Strike - Southwest island off the coast of Iki Island
The final Bamboo Strike requires some work to reach. If you head to the far south of Iki Island (and west from the previous Strike), you’ll spot an island. Climb down the cliff to reach the shore and then swim across to the southern point of the island.