Unwritten Tales are short Iki Island encounters with no map marker and no journal entry. You stumble on them while exploring, and the ones listed as Common Courtesy in the Collections menu count toward the Common Courtesy trophy.
Part 16 of 16 in Tales of Iki
Bury Ship Captain (northern coast of Yahata). Hachibee the Beekeeper (Old Gambler's Wood, Yahata). Helping Kodama (east of Lake Nagata, Gonoura). Saving Peasants From Lake (Buddha's Footprints, Gonoura). Raider Memorial Archery Challenge (Raider Memorial, Gonoura). Retelling Legends to Uta (east of Yahata Forest).
Two need extra prep. The archery challenge needs Tadayori's Armor from the Tsushima Mythic Tale, and Uta's tale needs the Legends story chapters finished. If the archery challenge does not tick off in the menu, start it again and it should register.
The Legend of Tadayori
The Legend of Tadayori is a Mythic Tale in Azamo, Izuhara, about a famous archer and the kami-blessed armour he wore. Finishing it gives you Tadayori's Armor, the set to wear if you fight mostly with a bow.
A Helping Hand
A Helping Hand is an Iki Island side tale where you keep running into Emotaro, a man rebuilding his home alone after the Mongols burned it. Help him four times and you get the Charm of Iron Grip.
A Mother's Law
A Mother's Law is an Iki Island side tale given by the raider leader Fune at Fune's Refuge in Yahata. It opens after Epilogue: Last Words and has you help her hit a Mongol supply ship.
A Raider's Return
A Raider's Return is an Iki Island tale where Tenzo takes Jin to meet his crew of raiders. It's how you first link up with the raiders, a group that normally has no love for samurai, in the fight against the Eagle Tribe.