Sentenced to death for the murder of millions of women, children, and men - guy is reborn into a magical world devoid of the previous horrors he experienced in his lifetime.
From what I can tell, this ‘manga’ is already developed fully and initially takes place in a modernized world; if you’re really interested in the entire story, the link for it is: http://royalroadl.com/fiction/807
Spectral Regalia