To unlock the seal of the middle device you need to activate all the surrounding five devices by using Geo elemental character to activate the devices, in order to activate all 5 together you need to follow the sequence shows in step 1. After you have activated all 5 devices the middle device seal will be unlock, after you have access it a path to the top will appear, on top there also one of the device that need Geo elemental character to activate, after you have activate the device you will be given 4 minutes to defeat all the enemy in order to clear this domain shows in step 2.