Please note I watched this stretched out over a few months, so my memory of the first half isn't reliable.

Violence/Gore: There is about one fight every episode but it's mostly between robots, some robots resemble humans although most do not. That said the robot body count is huge and the violence involves them getting torn apart/impaled/crushed/stabbed etc. Robots with human-like bodies will bleed realistically for the injuries they sustain.

Spoiler: When Casshern is injured he can regenerate but with a great deal of pain. It's particularly intense when he gets beaten up severely.

Nudity/Sexual content: In a dream episode Lyuze goes home with a man/robot and it's implied that she may have had sex with him, but not even that is very clear. In the same episode she and another female character are seen naked but it's stylized, barbie doll level of detail and not meant as fan service.

Theological & Negative themes: Death is a very prominent theme in this series, but the important thing is how different characters deal with it, whether it's with hope or despair or anything in between. Spoiler: Some characters are or achieve immortality.