There are seven Sunchildren in total for the player to find in Genshin Impact's Sunchildren Hide and Seek.
Finding all seven of them is necessary to complete this Hidden Exploration Objective. The main reason to do it is to unlock the hidden achievement, "The Children of God Shall Dance." Otherwise, it isn't integral for other quests in Enkanomiya.
Note: It must be Evernight to see the Sunchildren. It doesn't matter which NPC the player talks to first. All that matters is that the player talks to all seven Sunchildren.
Also, Elemental Sight will help players notice the Sunchildren at a distance.
Talking to Isumenasu involves a small puzzle to open the barrier leading to him.
When the player arrives here, they might notice several things:
Head to the Place of Essence first (it's east of the barrier). There should be a blueish aura surrounding the active character by now.
Afterward, climb to the left and activate the Day-Night Mechanism over there. It should now be Whitenight. After doing so, head down to where Isumenasu's barrier was to notice that the barrier is no longer there.
Isumenasu won't be there, but a gray structure should be nearby. Approach it, and the blueish aura from the active character should vanish. Once the Triangular Mechanism is formed, strike it once to move the western wall.
After that is done, head back to the Day-Night Mechanism above this room and swap back to Evernight.
Swap to Evernight and head back to the room down below. The barrier should still be gone, but Isumenasu should be there. There is also an Exquisite Chest to the left of Isumenasu. Open it for free rewards and talk to Isumenasu before proceeding to the next NPC.
Remember that every location can be accessed quickly from the southern Teleport
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