User blog comment:Xilinoc/Ch. 540 - The Sword Five/@comment-33447191-20130606193857/@comment-1351982-20130607205550

Engetsu (剡月) means scathing moon. Engetsu "scathing moon" resembles the word engetsu "crescent moon" (more lit. "dammed [and so curtailed] moon") cited above. So since Engetsu's release command is burn and it releases riatsu flames, Engetsu is probably a representation of the fires of Hell and eternal damnation.