In order to complete the quest, players will have to travel to Koseki Village on Seirai Island. As you reach the village, you will find hilichurls surrounding Fujiwara Toshiko, and you will have to defeat them to talk to her to trigger the quest.
Fujiwara Toshiko will give you a map that will help you in finding the treasure of her ancestors for her. After that, follow this guide to proceed through the Relics of Seirai world quest by solving puzzles.
Relics of the Serai Quest - Solve the Puzzle 1
After you talk to Fujiwara Toshiko, go to the location indicated on the map and activate the first puzzle.
Then, step on all the Japanese letters that appear on the wooden floor according to the pattern present on the treasure map.
You can also take the help of the image below to solve the puzzle.
Relics of the Serai Quest - Solve the Puzzle 2
After you solve the first puzzle, the path to the basement will open up, containing a bigger puzzle. After you go to the basement, start the puzzle from the wall.
Then, you need to follow the pattern shown in the image to solve the second puzzle.
Relics of the Serai Quest - Solve the Puzzle 3
After you solve the second puzzle, a dialogue will initiate, and then, you will have to solve the last puzzle of the quest.
Go to the wall to start the puzzle mechanism and follow the pattern shown in the image below to solve it.
After that, the chest next to it will get unlocked for you to collect the items in it.