There are three Haiku locations 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 award you a headband based on your Haiku composed.
Waterfall Haiku - Lone Spirit Falls
This Haiku can be located by heading to Lone Spirit Falls, located south of the Sentinel’s Peak Mongol Territory.
Mountainside Haiku - East of Minato’s Camp
The next Haiku can be located by heading to Minato’s Camp, on the east of Mount Takenotsuji, and continuing to the east.
Wisteria Haiku - Senjo Gorge
The final Haiku is located at Senjo Gorge, reach it by heading west from the Cloud Forest Temple or north from Kazumasa’s End.