Tsurumi Island is an island introduced in Genshin Impact update 2.2 for the Inazuma region. This questline is the final part of the "Through the Mist" questline which requires you to travel to Tsurumi Island. You can find the guide for the second part of this questline here. Completing this questline will unlock the Tsurumi Island and subquests on the island.
The Sun-Wheel and Mt.Kanna Quest Guide
The first step you want to do is to travel to Tsurumi Island using a Waverider in Ritou island. After reaching the island, unlock the Statue of Seven waypoint for easier access. You will notice that the island is filled with fog, preventing you from seeing the entire island. Go to the quest area and talk to the NPC called Kama. After talking to Kama, travel further into the island and the fog around the island will disappear.
Travel down to Wakukau Shoal and make sure to avoid the thunder hitting the ground. Once you are in the quest area, use the feather on the bird statue to your left. Defeat the enemies that spawn and touch the feather that appears.
Head to Oina Beach
After the cutscene, use the teleport waypoint in the Autake plains and go to Oina beach. Use the feather on the thunderbird statue near the tree and be prepared to fight some Ruin Sentinels. After defeating the enemies, touch the feather that appears once again. After the cutscene ends, use the teleport waypoint in Autake plains again and go south to the quest area.
Head to Autake Plains
Defeat the Rifthound monsters that appear when you reach the quest area. Use the feather on the thunderbird statue that is not lit up and touch the feather near the stone pillar. Wait for the cutscene and head for Mt. Kanna. You can climb the mountain by going to the hollow area near the Wakukau Shoal.
Investigate the altar inside Mt.Kanna and be prepared to fight the Thunder Manifestation. The area is small so try to bring characters like Ayaka or Mona so you can avoid its attacks. Once you defeat the Thunderbird, use the feather near Ruu and touch the feather that appears. Go back to Ruu and talk to him after the cutscene to continue with the story.
Go to Seirai Island
After taking Ruu, use the teleport waypoint near the quest area. Once the cutscene ends, return to Mt. Kanna to return the feathers. Talk to Ruu and teleport back to Inazuma City and report back to Sumida. Go to Kiminami Restaurant and talk to Sumida again to complete the quest. Completing the quest will give you the "Thunder is Forever" achievement, 40 Primogems, and 3 Hero's Wit as a reward.