I made some changes to this Moc since I first posted this so here is a current picture:
I needed to make this after I saw the picture of him in "The art of Bionicle":
This is his torso construction from the back:
The only modification is the paint on the mask, everything else are normal Lego parts.
I used the transparent red pieces in his torso, because hints of it are visible in the concept art.
This moc surely could still be improved but I don´t have the pieces I would need for that.