Similar to the other Inazuma domains, Shakkei Pavilion and Empty Boat of a Thousand Gates, Formation Estate is not instantly accessible. To make this domain appear, you'll first need to stop the lightning storms around Jakotsu Mine. This can be accomplished by completing the world quest Orobashi's Legacy: Part III.
For help in progressing this series, see our Orobashi's Legacy guides below:
Once you've finished Orobashi's Legacy: Part III, head towards the Formation Estate domain at the location marked below.
Ending the rainy weather in this area will make it possible to light the torches in front of the hidden domain. You'll see a Seelie hovering over an unlit torch; when pursued, the Seelie will move onto the next torch and then repeat this process.
Follow the Seelie and light each torch it stops at. Once all torches have been set ablaze, the key mechanism will unlock. Interact with this device to make Formation Estate appear.