I thought up the best edge. He stabs himself in the heart to use as a scabbard while he switches to using his monstrous clawed fists. Normally they are human with sharp nails but he transforms a bit until a more edgy form when near death, which is why he must stab himself there and keep it there so he remains near death. Perhaps he heals too fast to remain in monster form for long otherwise.

Not so sure about the psycho comment. I'm sure some soldiers remain optimistic and happy rather than all of them turning into edgelord. Unless you mean you can't be happy while actually fighting without being a psycho, which does make sense. Evvie is serious when fighting life or death rather than giggling, for example, but remains happy and optimistic otherwise unless someone manages to piss her off. She fights monsters mostly rather than killing sentient beings, which would do more harm to the psyche, although she would do so regardless if necessary. Justification of killing helps the psyche a lot, I'm sure.