Embracing the darkness metaphor (spoilers)
Nobuo talked about 'embracing the darkness' or something along these lines. Perhaps as a matter of survival. He said this while in the tunnel, and when he appeared during Teru's hallucinations. However it did not seem to connect or resolve by the end of the film. It seems that Teru rejected 'embracing darkness' as part of his intent for Ako and himself to survive, when facing the volcano at the end.
Any ideas?
Did the manga delve deeper into this?
p.s. Nobuo's facial makeup was quite interesting. It is like he regressed to a more primitive, primordial state.