For the Ready Player Zero Achievement in Genshin Impact you will need to place a game of Hide and Seek with a character called Childish Jiang. You can find him in the north of Mt. Tianhend near Liyue Harbor. When you speak with him, he will ask you if you want to play a game with him.
He will hide in four places, and each time you will have slightly less time to find him.
Hiding Place 1
The first hiding place is up the ridge from where you find him. The ridge is split into a lower section, a short cliff face, and a higher section. He will be hiding behind a boulder on the higher section.
Hiding Place 2
For the second hiding place, continue to run up the higher ridge, and he will be hiding behind the first of two trees on the left.
Hiding Place 3
Fron from the tree, head to the east and you will be able to and you will see a small house with a stone structure behind it. Childish Jiang is hiding behind the house on the right side.
Hiding Place 4
For the fourth hiding place, head directly towards the orange tree you can see through the small alley beside the house. You will come to a cliff face, and if you turn right you will see him hiding behind another boulder.
Once you find him the fourth time, you will complete the Ready Player Zero achievement. If you fail to find him at any point, you will just need to repeat that step, not the entire quest.