As one of the many hidden achievements in Genshin Impact, the Shuumatsu Gaiden can only be achieved and triggered when you discover something while exploring the vast world of Teyvat. For this certain achievement, no clues and navigation marks are provided to complete the missions. It will not even be listed on your quest window.
One of the things to note is that this hidden achievement utilizes the mechanic where players need to wait another real-life day to proceed to the next task. You need to complete five tasks, and only one task can be done per day. So make sure to do and complete the tasks on consecutive days not to waste time.
To start this five-day mission series, teleport to Araumi and go to the camp indicated on the map below.
The area will be lurking with Fatui Skirmishers, so be prepared to fight.
After defeating the enemies, go to the camp and pick up the tattered notes inside.
The writings are messed up, but Paimon can read a few lines that say “…when deciphering the slip, the secret code…” and “…the first half is ‘In the middle of a hazy night’….” Based on these, Paimon will suggest that next time you get and decipher a fortune slip from the Grand Narukami Shrine, you should try to match the secret codes.
Go to the Grand Narukami Shrine and take a bamboo slip or fortune slip.
After drawing a fortune slip, talk to Gendou Ringo, and instead of getting the slip deciphered, select the choice that says “(Hand over the fortune slip) In the middle of a hazy night.”
Gendou Ringo will respond with “Cloudy” and hand you a strip of paper.
Unlike the usual paper with your fortune written on it, this one-handed to you is a Strange Fortune Slip. It contains a photo of a location, information about misconduct, and a line that says, “Send in the Shuumatsu to end traitors and criminals alike.”
Go to the location indicated on the paper, which is the cave under Inazuma City.
You will find Fireblade Mourisu Boris, a Fatui Pyro Agent with two Pyroslinger Bracers.
Defeat these felons to complete the mission.
To get the mission for the second day, head back to the Grand Narukami Shrine, take a fortune slip, and choose the second option when talking to Gendou Ringo instead of having the slip deciphered.
Paimon will notice the slight change in Gendou Ringo’s character when she does not call the fortune slip “strips of paper.” She also responded “Foggy” instead of “Cloudy.”
The Strange Fortune Slip will indicate another photo of a location and the mission details.
Based on the photo, the designated area is the tidal flat near the Kujou Encampment. It is on the west side, just below the Teleport Waypoint.
You have to find and defeat Makita Unio, also known as Mousey Maki.
For the third day, the mission is called “Birds of a Feather,” and you will have to ambush the thieves during their meeting.
The cave is beneath Inazuma City, but there is a designated hour this time. The meeting will occur “late night and end sometime before dawn.”
Before entering the cave, adjust your in-game time to somewhere between 20:00 and 24:00.
Four enemies will be there, and you have to defeat them all.
The mission for the fourth day is titled “End of a 30-Year Cold Case: Demonbane Kin,” as indicated in the Strange Fortune Slip.
You have to find and defeat Matsudaira Kinjirou, nicknamed “Demonbane Kin,” and his accomplices who have been spotted in the southern parts of Yashiori Island.
The exact location is near the Teleport Waypoint at the southern end of Yashiori Island.
After teleporting, walk a little to the west, and in the cave, you will find some Nobushis.
Defeat them and investigate the campfire cooking pot.
Paimon will suggest following the shoreline, and you have to walk by the cliff to the west until you get to the beach where there are more Nobushis.
A little beyond that, one samurai is resting on a flat rock. That is Demonbane Kin.
Defeat him to complete this day’s mission.
When you go back to the Grand Narukami Shrine to take another mission, you will find that Gendou Ringo is nowhere to be found. However, you have to investigate a slip on the counter.
The note, left by someone, indicates that it is the thieves’ final destination and that you have to investigate the strange occurrences there.
Included in the note is a map with a marked location.
The broken bridge is a little north of the shrine, just below the mountain.
You can glide down or teleport to the Court of Flowing Sand domain entrance and walk to the broken bridge.
Upon arriving at the location, you were suddenly attacked by someone, and you lost consciousness.
You will wake up in a cage inside a cave and find out that it was Gendou Ringo’s doing. She will interrogate you about your identity and how you got knowledge about the Shuumatsuban’s secret code.
After explaining everything, Gendou Ringo will understand, and she will also tell you that the Gendou who gave you the missions from the second day is an impostor and that she had to fake her death to avoid getting caught the Fatui spies.
Gendou Ringo will then propose that you work as an external member of the Shuumatsuban, an organization in Inazuma under the Yashiro Commission.
Agreeing will unlock the hidden achievement SHUUMATSU GAIDEN and open the cage. You will also have access to the treasures inside this cave.