Hello, I've gone to the ether after placing the key and I'm being chased by the spirit and I can't get through it. How can I defeat this thing or bypass it?

You can't defeat him. His nature and motives will be revealed to you later as the plot progresses. The goal in the Ether section is to find two energy balls (one should be near the centre of the arena) and carry each to the round pedestal next to the vortex in the centre while avoiding the spirit. Once you place both, you can jump into the vortex to escape. The spirit will disappear and reappear randomly. If he spots you, he will start moving faster to catch you. If that happens, drop the ball and run around the maze until he disappears or loses track of you (monitor the sound of the footsteps).

It's tough, but I'm in a situation where I have to do the segment every time I want to save the game (God difficulty).

EDIT: The Sight (augmented vision) will help you spot the energy balls through walls. It's easier if you try to sneak as much as you can while getting to the ball.