The Octave of Maushiro is the second part of the "Through the Mist" questline. You can only unlock this quest after completing the "A Particularly Particular Author" quest. Just like the first part, Sumida will be the one who gives you the quest. However, you have to wait until the server resets after completing the "A Particularly Particular Author" quest before you can start the Octave of Maushiro quest.

Beginning the Quest

Octave Of Maushiro Guide For Genshin Impact
Octave Of Maushiro Guide For Genshin Impact

After the server resets, go back to Sumida in Inazuma City. She has gathered all the adventurers that were affected by the Maushiro incident. All of them will share what they have experienced on Tsurumi Island and talk about how their memory is blurry. Sumida asks you once more to travel to Tsurumi Island and get a hold of the Maushiro. Teleport back to the Tsurumi Island using the Statue of Seven waypoint. Travel to Tsurumi Island After arriving at Tsurumi Island, you will notice that the fog on the island is back, and you have to rely on the lamps again.

Octave Of Maushiro Guide For Genshin Impact