Carnage

Carnage or Shura is a concept associated with the Divergent Laws or the demon sword Kernviter specifically.

It suggests an experience of being different from the experience of being a human, in which the latter can take the form of the former without reverting back to the latter again.

Background
Before Leonhardt accepted Kernviter from the Grandmaster, his mentor and Anguis No. VII, Arianrhod, warned him that his "self would be reborn as carnage and he would never be able to return to his human self".

It is thought his decision to embark on the path of Carnage is the reason why Leonhardt stopped ageing and his age has always been published as "?" in official works.

Translation
Since there is virtually no information available on Carnage, it is difficult to find an appropriate translation for the term -- or to conclude with certainty whether it can be considered as a term at all.

In the localisation of Trails in the Sky SC, it was not translated using a specific term. For example, during the fight with Leonhardt on top of the Axis Pillar, Liber Ark, Carnage is mentioned four times and each time translated differently.
 * 1) Original line: もし、お前たちの覚悟が俺の 修羅 を上回っているのなら……

Localisation: If you feel the strength of your conviction is stronger than my own...
 * 1) Original line: ……なかなかやるが俺の 修羅 を止めるほどではない.

Localisation: You've done well, but not well enough to match my power.
 * 1) Original line:『理』に至りでもしなければ『 修羅 』に届く道理はない.

Localisation: Only those who have attained enlightenment can hope to match one such as myself.
 * 1) Original line: そのためには…… 修羅 と化しても悔いはない.

Localisation: And I have no regrets for what I've become in pursuit of my goal.