We'll I'm not really sure but it sounds good.
You have to use a very hard distorsion to play this song.
It's very easy.
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|-00000-121-00000-323-------------|
[ Tab from: https://www.guitartabs.cc/tabs/t/therion/return_tab.html ]
Here it is. I don't think they are playing on the 2 or 3 first strings because it will sound
too high-pitched.But if you want you can play this song like this:
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|-2-2-2-2-2-3-4-3--2-2-2-2-2-5-4-5--|
|-0-0-0-0-0-1-2-1--0-0-0-0-0-3-2-3--|
This is the main riff:I love it!!