I would really to know, because there seems to be a couple of mechanics that were not really explained in the tutorial. Also, a manual, if it does exist, would be quite the 90's thing as well.

Short answer: no.

Despite manuals being a 90's thing, part of the "insane difficulty" is not knowing what things do beforehand (or at all, if you can't figure them out yourself), and for the most part they've stuck to their guns about that. They only begrudgingly included descriptions for items you buy in the store in a later patch.