User blog comment:Disfigure/This was only shown in the Anime about Guren Ichinose/@comment-25942629-20160208212128/@comment-24726063-20160208230146

Like ResidentialPsycho said, in the light novel Guren can turn his sword red and it is some normal katana (not demon) by using magic insignias on the sword sheet. I even think they mentioned this was an Ichinose family technique and if I am right this is even in the first volume.